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general description the MAX1565 provides a complete power-supply solution for digital still and video cameras through the integration of ultra-high-efficiency step-up/step-down dc-to-dc con- verters along with three auxiliary step-up controllers. the MAX1565 is targeted for applications that use either 2 or 3 alkaline or nimh batteries as well as those using a single lithium-ion (li+) battery. the step-up dc-to-dc converter accepts inputs from 0.7v to 5.5v and regulates a resistor-adjustable output from 2.7v to 5.5v. it uses internal mosfets to achieve 95% efficiency. adjustable operating frequency facili- tates design for optimum size, cost, and efficiency. the step-down dc-to-dc converter can produce output voltages as low as 1.25v and also utilizes internal mosfets to achieve 95% efficiency. an internal soft- start ramp minimizes surge current from the battery. the converter can operate from the step-up output pro- viding buck-boost capability with up to 90% compound efficiency, or it can run directly from the battery if buck- boost operation is not needed. the MAX1565 features auxiliary step-up controllers that power ccd, lcd, motor actuator, and backlight cir- cuits. the device also features low-cost expandability by supplying power, an oscillator signal, and a refer- ence to the max1801 sot23 slave controller that sup- ports step-up, sepic, and flyback configurations. the MAX1565 is available in a space-saving 32-pin thin qfn package. applications digital still cameras digital video cameras pdas features step-up dc-to-dc converter 95% efficient 3.3v (fixed) or 2.7v to 5.5v (adjustable) output voltage step-down dc-to-dc converter operate from battery for 95% efficient buck combine with step-up for 90% efficient buck- boost adjustable output down to 1.25v three auxiliary pwm controllers up to 1mhz operating frequency 1? shutdown mode internal soft-start control overload protection compact 32-pin, 5mm x 5mm thin qfn package MAX1565 small, high-efficiency, five-channel digital still camera power supply ________________________________________________________________ maxim integrated products 1 MAX1565 5mm x 5mm thin qfn top view 32 28 29 30 31 25 26 27 comp2 gnd dl1 dl2 fb2 dl3 outsub fb3 10 13 15 14 16 11 12 9 on1 on3 on2 ref onsu compsu fbsu fbselsu 17 18 19 20 21 22 23 sdok 24 comp3 outsua lxsu pgndb osc fbsel1 fbselsd 2 3 4 5 6 7 8 fbsd compsd onsd insd lxsd pgnda fb1 1 comp1 pin configuration ordering information main +3.3v core +1.5v motor +5v ccd +15v/-7.5v lcd, led +15v step-up step-down aux1 aux2 aux3 0n3 on2 on1 onsd onsu MAX1565 input +0.7v to +5.5v on/off controls typical operating circuit 19-2712; rev 0; 1/03 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. evaluation kit available part temp range pin-package MAX1565etj -40? to +85? 32 thin qfn
MAX1565 small, high-efficiency, five-channel digital still camera power supply 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v outsu = 3.3v, t a = 0? to +85? , unless otherwise noted.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. outsu_, insd, sdok, on_, fb_, fbsel_ to gnd ....................................................-0.3v to +6v pgnd to gnd .......................................................-0.3v to +0.3v dl_ to pgnd...........................................-0.3v to outsu + 0.3v lxsu current (note 1) ..........................................................3.6a lxsd current (note 1) ........................................................2.25a ref, osc, comp_ to gnd.....................-0.3v to outsu + 0.3v continuous power dissipation (t a =+70?) 32-pin thin qfn (derate 22mw/? above +70 c).............................................................1700mw operating temperature range ...........................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? note 1: lxsu has internal clamp diodes to outsu and pgnd, and lxsd has internal clamp diodes to insd and pgnd. applications that forward bias these diodes should take care not to exceed the devices power dissipation limits. parameter conditions min typ max units general input voltage range (note 2) 0.7 5.5 v minimum startup voltage i load < 1ma, t a = +25 c, startup voltage tempco is -2300ppm/ c (typ) (note 3) 0.9 1.1 v overload protection fault interval 100,000 osc cycles thermal shutdown 160 c thermal-shutdown hysteresis 20 c shutdown supply current into outsu onsu = onsd = on1 = on2 = on3 = 0; outsu = 3.6v 0.1 5 a step-up dc-to-dc supply current into outsu onsu = 3.35v, fbsu = 1.5v (does not include switching losses) 290 400 a step-up plus 1 aux supply current into outsu onsu = on_ = 3.35v, fbsu = 1.5v, fb_ = 1.5v (does not include switching losses) 420 600 a step-up plus step-down supply current into outsu onsu = onsd = 3.35v, fbsu = 1.5v, fbsd = 1.5v (does not include switching losses) 470 650 a reference output voltage i ref = 20a 1.23 1.25 1.27 v reference load regulation 10a < i ref < 200a 4.5 10 mv reference line regulation 2.7 < outsu < 5.5v 1.3 5 mv osc discharge trip level rising edge 1.225 1.25 1.275 v osc discharge resistance osc = 1.5v, i osc = 3ma 52 80 ? osc discharge pulse width 300 ns osc frequency r osc = 40k ? , c osc = 100pf 400 khz step-up dc-to-dc converter step-up startup-to-normal operating threshold rising or falling edge (note 4) 2.30 2.5 2.60 v step-up startup-to-normal operating threshold hysteresis 80 mv
MAX1565 small, high-efficiency, five-channel digital still camera power supply _______________________________________________________________________________________ 3 electrical characteristics (continued) (v outsu = 3.3v, t a = 0 c to +85 c , unless otherwise noted.) parameter conditions min typ max units step-up voltage adjust range 2.7 5.5 v fbsu regulation voltage 1.231 1.25 1.269 v outsu regulation voltage fbselsu = gnd 3.296 3.35 3.404 v fbsu to compsu transconductance fbsu = compsu 80 135 185 s fbsu input leakage current fbsu = 1.25v -100 +1 +100 na idle-mode trip level (note 6) 150 200 265 ma current-sense amplifier transresistance 0.3 v/a step-up maximum duty cycle fbsu = 1v 80 85 90 % outsu leakage current v lx = 0v, outsu = 5.5v 0.01 20 a lxsu leakage current v lxsu = v out = 5.5v 0.01 20 a n-channel 95 150 switch on-resistance p-channel 150 250 m ? n-channel current limit 1.6 2 2.4 a p-channel turn-off current 20 ma startup current limit outsu = 1.8v (note 5) 800 ma startup t off outsu = 1.8v 700 ns startup frequency outsu = 1.8v 200 khz step-down dc-to-dc converter fbsd regulation voltage 1.231 1.25 1.269 v outsd regulation voltage fbselsd = gnd 1.48 1.5 1.52 v fbsd to compsd transconductance fbsd = compsd 80 135 185 s fbsd input leakage current fbsd = 1.25v -100 +1 +100 na idle-mode trip level (note 6) 110 160 190 ma current-sense amplifier transresistance 0.60 v/a v lxsd = 5.5v, outsu = 5.5v 0.01 20 lxsd leakage current v lxsd = 0v, outsu = 5.5v 0.01 20 a n-channel 95 150 switch on-resistance p-channel 150 250 m ? p-channel current limit 0.7 0.79 1.0 a n-channel turn-off current 20 ma soft-start interval 4096 osc cycles sdok output low voltage fbsd = 0.4v; 0.1ma into sdok pin 0.002 0.1 v sdok operating voltage range 1.0 5.5 v idle mode is a trademark of maxim integrated products, inc.
MAX1565 small, high-efficiency, five-channel digital still camera power supply 4 _______________________________________________________________________________________ electrical characteristics (continued) (v outsu = 3.3v, t a = 0 c to +85 c , unless otherwise noted.) parameter conditions min typ max units auxiliary dc-to-dc controllers (aux 1, 2, and 3) maximum duty cycle fb_ = 1v 80 85 90 % fb_ regulation voltage fb_ = comp_ 1.231 1.25 1.269 v fb_ to comp_ transconductance fb_ = comp_ 80 135 185 s fb_ input leakage current fb_ = 1.25v -100 +1 +100 na aux1 output regulation voltage fbsel1 = gnd, fb1 connected directly to aux1 output 4.93 5 5.07 v output high 3 10 dl_ driver resistance output low 2 5 ? dl_ drive current sourcing or sinking 0.5 a soft-start interval 4096 osc cycles logic inputs (on_ , fbsel_) 1.1v < outsu < 1.8v (onsu only) 0.2 input low level 1.8v < outsu < 5.5v 0.4 v 1.1v < outsu < 1.8v (onsu only) v outsu - 0.2 input high level 1.8v < outsu < 5.5v 1.6 v fbsel = 3.6v, outsu = 3.6v -100 0 +100 fbsel_ input leakage current fbsel = gnd, outsu = 3.6v -100 0 +100 na on_ impedance to gnd on_ = 3.35v 330 k ? electrical characteristics (v outsu = 3.3v, t a = -40 c to +85 c , unless otherwise noted.) parameter conditions min typ max units general input voltage range (note 2) 0.7 5.5 v minimum startup voltage i load < 1ma, t a = +25 c, startup voltage tempco is -2300ppm/ c (typ) (note 3) 1.1 v shutdown supply current into outsu onsu = onsd = on1 = on2 = on3 = 0 outsu = 3.6v 5 a step-up dc-to-dc supply current into outsu onsu = 3.35v, fbsu = 1.5v (does not include switching losses) 400 a step-up plus 1 aux supply current into outsu onsu = on_ = 3.35v, fbsu = 1.5v, fb_ = 1.5v (does not include switching losses) 600 a step-up plus step-down supply current into outsu onsu = onsd = 3.35v, fbsu = 1.5v, fbsd = 1.5v (does not include switching losses) 650 a reference output voltage i ref = 20a 1.23 1.27 v reference load regulation 10a < i ref < 200a 10 mv
MAX1565 small, high-efficiency, five-channel digital still camera power supply _______________________________________________________________________________________ 5 electrical characteristics (continued) (v outsu = 3.3v, t a = -40 c to +85 c , unless otherwise noted.) parameter conditions min typ max units reference line regulation 2.7v < outsu < 5.5v 5 mv osc discharge trip level rising edge 1.225 1.275 v osc discharge resistance osc = 1.5v, i osc = 3ma 80 ? step-up dc-to-dc converter step-up startup-to-normal operating threshold rising or falling edge (note 4) 2.30 2.60 v step-up voltage adjust range 2.7 5.5 v fbsu regulation voltage 1.225 1.275 v outsu regulation voltage fbselsu = gnd 3.283 3.417 v fbsu to compsu transconductance fbsu = compsu 80 185 s fbsu input leakage current fbsu = 1.25v -100 +100 na idle-mode trip level (note 6) 150 275 ma step-up maximum duty cycle fbsu =1v 80 90 % outsu leakage current v lx = 0v, outsu = 5.5v 20 a lxsu leakage current v lxsu = v out = 5.5v 20 a n-channel 150 switch on-resistance p-channel 250 m ? n-channel current limit 1.6 2.4 a step-down dc-to-dc converter fbsd regulation voltage 1.225 1.275 v outsd regulation voltage fbselsd = gnd 1.47 1.53 v fbsd to compsd transconductance fbsd = compsd 80 185 s fbsd input leakage current fbsd = 1.25v -100 +100 na idle-mode trip level (note 6) 110 195 ma v lxsd = 5.5v, outsu = 5.5v 20 lxsd leakage current v lxsd = 0v, outsu = 5.5v 20 a n-channel 150 switch on-resistance p-channel 250 m ? p-channel current limit 0.7 1.0 a sdok output low voltage fbsd = 0.4v; 0.1ma into sdok pin 0.1 v sdok operating voltage range 1 5.5 v auxiliary dc-to-dc controllers (aux 1, 2, and 3) maximum duty cycle fb_ = 1v 80 90 % fb_ regulation voltage fb_ = comp_ 1.225 1.275 v
MAX1565 small, high-efficiency, five-channel digital still camera power supply 6 _______________________________________________________________________________________ electrical characteristics (continued) (v outsu = 3.3v, t a = -40 c to +85 c , unless otherwise noted.) parameter conditions min typ max units fb_ to comp_ transconductance fb_ = comp_ 80 185 s fb_ input leakage current fb_ = 1.25v -100 +100 na aux1 output regulation voltage fbsel1 = gnd, fb1 connected directly to aux1 output 4.90 5.10 v output high 10 dl_ driver resistance output low 5 ? logic inputs (on_, fbsel_) 1.1v < outsu < 1.8v (onsu only) 0.2 input low level 1.8v < outsu < 5.5v 0.4 v 1.1v < outsu < 1.8v (onsu only) v outsu -0.2 input high level 1.8v < outsu < 5.5v 1.6 v fbsel = 3.6v, outsu = 3.6v -100 +100 fbsel_ input leakage current fbsel = gnd, outsu = 3.6v -100 +100 na note 2: the ic is powered from the outsu output. note 3: since the part is powered from outsu, a schottky rectifier, connected from the input battery to outsu, is required for low-voltage startup. note 4: the step-up regulator operates in startup mode until this voltage is reached. do not apply full load current during startup. note 5: the step-up current limit in startup refers to the lxsu switch current limit, not an output current limit. note 6: the idle-mode current threshold is the transition point between fixed-frequency pwm operation and idle-mode operation (where switching rate varies with load). the spec is given in terms of inductor current. in terms of output current, the idle- mode transition varies with input/output voltage ratio and inductor value. for the step-up, the transition output current is approximately 1/3 the inductor current when stepping from 2v to 3.3v. for the step-down, the transition current in terms of output current is approximately 3/4 the inductor current when stepping down from 3.3v to 1.8v. step-up efficiency vs. load current (5v output) MAX1565 toc01 load current (ma) efficiency (%) 100 10 10 20 30 40 50 60 70 80 90 100 0 1 1000 v in = 4v v in = 3.6v v in = 3v v in = 2v v in = 1.5v v out = 5v step-up efficiency vs. load current (3.3v output) MAX1565 toc02 load current (ma) efficiency (%) 100 10 10 20 30 40 50 60 70 80 90 100 0 1 1000 v in = 3.6v v in = 3v v in = 2v v in = 1.5v v out = 3.3v step-down efficiency vs. load current MAX1565 toc03 load current (ma) efficiency (%) 100 10 10 20 30 40 50 60 70 80 90 100 0 1 1000 v in = 4.2v v in = 3.6v v in = 3v insd connected to battery v out = 1.5v does not include current used by the step-up to power the ic typical operating characteristics (circuit of figure 1, t a = +25 c, unless otherwise noted.)
MAX1565 small, high-efficiency, five-channel digital still camera power supply _______________________________________________________________________________________ 7 buck-boost efficiency vs. load current (1.5v output, v outsu = 3.3v) MAX1565 toc04 load current (ma) efficiency (%) 100 10 10 20 30 40 50 60 70 80 90 100 0 1 1000 v in = 3v v in = 2v v in = 1.5v v outsd = 1.5v v outsu = 3.3v buck-boost efficiency vs. load current (3.3v output, v outsu = 5v) MAX1565 toc05 load current (ma) efficiency (%) 100 10 10 20 30 40 50 60 70 80 90 100 0 1 1000 v in = 4.2v v in = 3.6v v in = 3v v in = 2v v in = 1.5v v outsd = 3.3v v outsu = 5v buck-boost efficiency vs. input voltage (1.5v output, v outsu = 3.3v) MAX1565 toc06 input voltage (v) efficiency (%) 3.5 3.0 2.5 2.0 10 20 30 40 50 60 70 80 90 100 0 1.5 4.0 i outsd = 250ma i outsd = 500ma i outsd = 100ma v outsd = 1.5v v outsu = 3.3v buck-boost efficiency vs. input voltage (3.3v output, v outsu = 5v) MAX1565 toc07 input voltage (v) efficiency (%) 4.0 3.5 3.0 2.5 2.0 10 20 30 40 50 60 70 80 90 100 0 1.5 4.5 i outsd = 250ma i outsd = 500ma i outsd = 100ma v outsd = 3.3v v outsu = 5v boost and buck-boost combined efficiency vs. input voltage MAX1565 toc08 input voltage (v) efficiency (%) 3.0 2.5 2.0 1.5 60 70 80 90 100 50 1.0 3.5 v outsu = 3.3v, 200ma v outsd = 1.5v, 200ma eff% = [(v su i su ) + (v sd i sd )]/(v in i in ) aux_ efficiency vs. load current (5v output) MAX1565 toc09 load current (ma) efficiency (%) 100 10 10 20 30 40 50 60 70 80 90 100 0 1 1000 v in = 3.6v v in = 3v v in = 2v v in = 1.5v v outaux_ = 5v no-load input current vs. input voltage (switching) MAX1565 toc10 input voltage (v) input current (ma) 4 3 2 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 15 v outsd = 1.5v v outsu = 5v buck-boost (step-up and step down) step-up minimum startup voltage vs. load current (outsu) MAX1565 toc11 load current (ma) minimum startup voltage (v) 900 600 300 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 0 1200 *schottky diode connected from in to outsu with schottky* without schottky* typical operating characteristics (continued) (circuit of figure 1, t a = +25 c, unless otherwise noted.)
MAX1565 small, high-efficiency, five-channel digital still camera power supply 8 _______________________________________________________________________________________ typical operating characteristics (continued) (circuit of figure 1, t a = +25 c, unless otherwise noted.) reference voltage vs. temperature MAX1565 toc12 temperature ( c) reference voltage (v) 75 50 25 0 -25 1.241 1.242 1.243 1.244 1.245 1.246 1.247 1.248 1.249 1.240 -50 100 reference voltage vs. reference load current MAX1565 toc13 reference load current ( a) reference voltage (v) 200 150 100 50 1.245 1.246 1.247 1.248 1.249 1.250 1.251 1.244 0 250 oscillator frequency vs. r osc MAX1565 toc14 r osc (k ? ) oscillator frequency (khz) 100 10 100 200 300 400 500 600 700 800 900 0 1 1000 c osc = 470pf c osc = 220pf c osc = 100pf c osc = 47pf aux_ maximum duty cycle vs. frequency MAX1565 toc15 frequency (khz) maximum duty cycle (%) 900 800 100 200 300 500 600 400 700 81 82 83 84 85 86 87 88 80 0 1000 c osc = 100pf when this duty cycle is exceeded for 100,000 clock cycles, the MAX1565 shuts down step-up startup response MAX1565 toc16 100 s/div i outsu 100ma/div onsu 5v/div i in 1a/div outsu 2v/div 0v 0v 0a 0a v outso = 3.3v v in = 2v buck-boost startup response MAX1565 toc17 4ms/div outsd 500ma/div onsd = onsu 5v/div i outsd 200ma/div outsu 1v/div 0v 0v 0v 0a v outsu = 3.3v v outsd = 1.5v v in = 2.5v aux_ startup response MAX1565 toc18 2ms/div on1 5v/div i out 1 200ma/div out1 2v/div 0v 0v 0a v out1 = 5v v in = 2.5v
MAX1565 small, high-efficiency, five-channel digital still camera power supply _______________________________________________________________________________________ 9 step-up load transient response MAX1565 toc19 400 s/div i outsu 200ma/div v outsu ac-coupled 100mv/div 0a 0v v outsu = 3.3v v in = 2.5v step-down load transient response MAX1565 toc20 400 s/div i outsd 100ma/div v outsd ac-coupled 50mv/div 0a 0v v outsd = 1.5v v outsu = 3.3v v in = 2.5v typical operating characteristics (continued) (circuit of figure 1, t a = +25 c, unless otherwise noted.) pin description pin name function 1 comp1 auxiliary controller 1 compensation node. connect a series rc from comp1 to gnd to compensate the control loop. comp1 is actively driven to gnd in shutdown and thermal limit. 2 fb1 auxiliary controller 1 feedback input. for 5v output, short fbsel1 to gnd and connect fb1 to the output voltage. for other output voltages, connect fbsel1 to outsu and connect a resistive voltage-divider from the step-up converter output to fb1 to gnd. the fb1 feedback threshold is then 1.25v. this pin is high impedance in shutdown. 3 pgnda power ground. connect pgnda and pgndb together and to gnd with short trace as close to the ic as possible. 4 lxsd step-down converter power-switching node. connect lxsd to the step-down converter inductor. lxsd is the drain of the p-channel switch and n-channel synchronous rectifier. lxsd is high impedance in shutdown. 5 insd step-down converter input. insd can connect to outsu, effectively making outsd a buck-boost output from the battery. bypass to gnd with a 1f ceramic capacitor if connected to outsu. insd may also be connected to the battery, but should not exceed outsu by more than a schottky diode forward voltage. bypass insd with a 10f ceramic capacitor when connecting to the battery input. a 10k ? internal resistance connects outsu and insd. 6 onsd step-down converter on/off control input. drive onsd high to turn on the step-down converter. this pin has an internal 330k ? pulldown resistor. onsd does not start until outsu is in regulation. 7 c om p s d step-down converter compensation node. connect a series rc from compsd to gnd to compensate the control loop. compsd is pulled to gnd in normal shutdown and during thermal shutdown (see the step- down compensation section).
MAX1565 small, high-efficiency, five-channel digital still camera power supply 10 ______________________________________________________________________________________ pin description (continued) pin name function 8 fbsd step-down converter feedback input. for a 1.5v output, short fbselsd to gnd and connect fbsd to outsd. for other voltages, short fbselsd to outsu and connect a resistive voltage-divider from outsd to fbsd to gnd. the fbsd feedback threshold is 1.25v. this pin is high impedance in shutdown. 9 on1 auxiliary controller 1 on/off control input. drive on1 high to turn on. this pin has an internal 330k ? pulldown resistor. on1 cannot start until outsu is in regulation. 10 on2 auxiliary controller 2 on/off control input. drive on2 high to turn on. this pin has an internal 330k ? pulldown resistor. on2 cannot start until outsu is in regulation. 11 on3 auxiliary controller 3 on/off control input. drive on3 high to turn on. this pin has an internal 330k ? pulldown resistor. on3 cannot start until outsu is in regulation. 12 onsu step-up converter on/off control. drive onsu high to turn on the step-up converter. all other control pins are locked out until 2ms after the step-up output has reached its final value. this pin has an internal 330k ? resistance to gnd. 13 ref reference output. bypass ref to gnd with a 0.1f or greater capacitor. the maximum allowed load on ref is 200a. ref is actively pulled to gnd when all converters are shut down. 14 fbsu step-up converter feedback input. to regulate outsu to 3.35v, connect fbselsu to gnd. fbsu may be connected to outsu or gnd. for other output voltages, connect fbselsu to outsu and connect a resistive voltage-divider from outsu to fbsu to gnd. the fbsu feedback threshold is 1.25v. this pin is high impedance in shutdown. 15 compsu step-up converter compensation node. connect a series rc from compsu to gnd to compensate the control loop. compsd is pulled to gnd in normal shutdown and during thermal shutdown (see the step- down compensation section). 16 fbse ls u step-up feedback select pin. with fbselsu = gnd, outsu regulates to 3.35v. with fbselsu = outsu, fbsu regulates to a 1.25v threshold for use with external feedback resistors. this pin is high impedance in shutdown. 17 fbse ls d step-down feedback select pin. with fbselsd = gnd, fbsd regulates to 1.5v. with fbselsd = outsu, fbsd regulates to 1.25v for use with external feedback resistors. this pin is high impedance in shutdown. 18 fbsel1 auxiliary controller 1 feedback select pin. with fbsel1 = gnd and fb1 regulates to 5v. with fbsel1 = outsu, fb1 regulates to 1.25v for use with external feedback resistors. this pin is high impedance in shutdown. 19 osc oscillator control. connect a timing capacitor from osc to gnd and a timing resistor from osc to outsu to set the oscillator frequency between 100khz and 1mhz. this pin is high impedance in shutdown. 20 pgndb power ground. connect pgnda and pgndb together and to gnd with short trace as close to the ic as possible. 21 lxsu step-up converter power-switching node. connect lxsu to the step-up converter inductor. lxsu is high impedance in shutdown. 22 outsua step-up converter output. outsua is the power output of the step-up converter. connect outsua to outsub at the ic. 23 sdok this open-drain output goes high impedance when the step-down has successfully completed soft-start.
MAX1565 small, high-efficiency, five-channel digital still camera power supply ______________________________________________________________________________________ 11 pin description (continued) pin name function 24 comp3 auxiliary controller 3 compensation node. connect a series resistor-capacitor from comp3 to gnd to compensate the control loop. comp3 is actively driven to gnd in shutdown and thermal limit. 25 fb3 auxiliary controller 3 feedback input. connect a resistive voltage-divider from the output voltage to fb3 to gnd. the fb3 feedback threshold is 1.25v. this pin is high impedance in shutdown. 26 outsub step-up converter output. outsub powers the MAX1565 and is the sense input when fbselsu is gnd and the output is 3.3v. connect outsua to outsub. 27 dl3 auxiliary controller 3 gate-drive output. connect the gate of an n-channel mosfet to dl3. dl3 swings from gnd to outsu and supplies up to 500ma. dl3 is driven to gnd in shutdown and thermal limit. 28 dl2 auxiliary controller 2 gate-drive output. connect the gate of an n-channel mosfet to dl2. dl2 swings from gnd to outsu and supplies up to 500ma. dl2 is driven to gnd in shutdown and thermal limit. 29 dl1 auxiliary controller 1 gate-drive output. connect the gate of an n-channel mosfet to dl1. dl1 swings from gnd to outsu and supplies up to 500ma. dl1 is driven to gnd in shutdown and thermal limit. 30 gnd quiet ground. connect gnd to pgnd as close to the ic as possible. 31 comp2 auxiliary controller 2 compensation node. connect a series resistor-capacitor from comp2 to gnd to compensate the control loop. comp2 is actively driven to gnd in shutdown and thermal limit. 32 fb2 auxiliary controller 2 feedback input. connect a resistive voltage-divider from the output voltage to fb2 to gnd to set the output voltage. the fb2 feedback threshold is 1.25v. this pin is high impedance in shutdown. exposed pad ep exposed underside metal pad. this pad must be soldered to the pc board to achieve package thermal and mechanical ratings. the exposed pad is electrically connected to gnd.
MAX1565 small, high-efficiency, five-channel digital still camera power supply 12 ______________________________________________________________________________________ MAX1565 dl1 fb1 2 h v in +1.5v to +4.2v 20 f 20 f osc compsu compsd comp1 comp2 comp3 onsu onsd on1 on2 on3 100pf gnd to outsu outsua dl3 fb3 dl2 fb2 sdok current- mode step-up fbsu lxsu ref +1.25v ref pgndb outsub aux2 v-mode step-up pwm aux1 v-mode step-up pwm aux3 v-mode step-up pwm to vin 90.9k ? 1m ? to v in 0.1 f fbselsu fbselsd fbsel1 1000pf 10k ? 36.5k ? +15v 20ma +ccd bias 5v 500ma -7.5v 20ma -ccd bias +15v 100ma lcd 47 f +1.5v 350ma core 3.35v 600ma main system 10 f 1 f 3.3 h to v in to step-down direct from battery 1 f 1 f t1 10 f 1 f 4.7 h 1m ? 90.9k ? insd current- mode step- down fbsd lxsd pgnda 22 f 4.7 h 1000pf 10k ? 0.01 f 20k ? 3300pf 25k ? 6800pf 47k ? figure 1. typical application circuit
MAX1565 small, high-efficiency, five-channel digital still camera power supply ______________________________________________________________________________________ 13 2.35v v outsu onsu vref 1v onsu refok die over temp fault in clk normal mode startup oscillator internal power ok 100,000 clock cycle fault timer ref to v ref 300ns one-shot startup timer step-up timer done (sussd) 1.25v reference to internal power osc compsu fbsu to v ref soft-start ramp generator compsd fbsd onsd sussd on_ sussd to v ref soft-start ramp generator comp_ fb_ fault current- mode dc-to-dc step-down fault one of 3 voltage-mode dc-to-dc controllers aux_ insd lxsd ref gnd outsub pgnd sdok dl_ fltall fltall fault current- mode dc-to-dc step-up outsua lxsu pgnd onsu fltall fltall figure 2. MAX1565 functional diagram
MAX1565 detailed description the MAX1565 is a complete digital still camera power- conversion ic. it can accept input from a variety of sources including single-cell li+ batteries, 2-cell alkaline or nimh batteries, as well as systems designed to accept both battery types. the MAX1565 includes five dc-to-dc converter channels to generate all required voltages: 1) synchronous rectified step-up dc-to-dc con- verter with on-chip mosfets this typically sup- plies 3.3v for main system power. 2) synchronous rectified step-down dc-to-dc con- verter with on-chip mosfets powering the step- down from the step-up output provides efficient (up to 90%) buck-boost functionality that supplies a reg- ulated output when the battery voltage is above or below the output voltage. the step-down can also be powered from the battery. 3) auxiliary dc-to-dc controller 1 typically used for 5v output for motor, strobe, or other functions as required. 4) auxiliary dc-to-dc controller 2 typically sup- plies lcd bias voltages with either a multi-output flyback transformer, or boost converter with charge- pump inverter. alternately may power white leds for lcd backlighting. 5) auxiliary dc-to-dc controller 3 typically sup- plies ccd bias voltages with either a multi-output flyback transformer, or boost converter with charge- pump inverter. the MAX1565 can also operate with max1801 slave dc- to-dc controllers if additional dc-to-dc converter chan- nels are required. all MAX1565 dc-to-dc converter channels employ fixed-frequency pwm operation. in addition to multiple dc-to-dc channels, the MAX1565 also includes overload protection, soft-start circuitry, adjustable pwm operating frequency, and a power-ok (pok) output to signal when the step-down converter output voltage (for cpu core) is in regulation. step-up dc-to-dc converter the step-up dc-to-dc converter channel generates a 2.7v to 5.5v output voltage range from a 0.9v to 5.5v battery input voltage. an internal switch and synchro- nous rectifier allow conversion efficiencies as high as 95% while reducing both circuit size and the number of external components. under moderate to heavy loading, the converter operates in a low-noise pwm mode with constant frequency. switching harmonics generated by fixed-frequency operation are consistent and easily filtered. the step-up is a current-mode pwm. an error signal (at compsu) represents the difference between the feed- back voltage and the reference. the error signal pro- grams the inductor current to regulate the output voltage. at light loads (under 75ma when boosting from 2v to 3.3v), efficiency is enhanced by an idle mode in which switching occurs only as needed to service the load. in this mode, the inductor current peak is limited to typically 200ma for each pulse. step-down dc-to-dc converter the step-down dc-to-dc converter channel is opti- mized for generating output voltages down to 1.25v. lower output voltages can be set by adding an addi- tional resistor (see the applications information sec- tion). an internal switch and synchronous rectifier allow conversion efficiencies as high as 95% while reducing both circuit size and the number of external compo- nents. under moderate to heavy loading, the converter operates in a low-noise pwm mode with constant fre- quency. switching harmonics generated by fixed-fre- quency operation are consistent and easily filtered. the step-down is a current-mode pwm. an error signal (at compsd) represents the difference between the feedback voltage and the reference. the error signal pro- grams the inductor current to regulate the output voltage. at light loads (under 120ma), efficiency is enhanced by an idle mode in which switching occurs only as needed to service the load. in this mode, the inductor current peak is limited to 150ma (typ) for each pulse. the step-down remains inactive until the step-up dc- to-dc is in regulation. this means that the step-down dc-to-dc on/off pin (onsd) is overridden by onsu. the soft-start sequence for the step-down begins 1024 osc cycles after the step-up output is in regulation. if the step-up, step-down, or any of the auxiliary con- trollers remains faulted for 200ms, all channels turn off. the step-down also features an open-drain sdok out- put that goes low when the output is in regulation. buck-boost operation the step-down input can be powered from the output of the step-up. by cascading these two channels, the step- down output can maintain regulation even as the battery voltage falls below the step-down output voltage. this is especially useful when trying to generate 3.3v from 1-cell li+ inputs, or 2.5v from 2-cell alkaline or nimh inputs, or when designing a power supply that must operate from both li+ and alkaline/nimh inputs. compound efficien- cies of up to 90% can be achieved when the step-up and step-down are operated in series. small, high-efficiency, five-channel digital still camera power supply 14 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note that the step-up output supplies both the step-up load and the step-down input current when the step- down is powered from the step-up. the step-down input current reduces the available step-up output cur- rent for other loads. direct battery step-down operation the step-down converter can also be operated directly from the battery as long as the voltage at insd does not exceed outsu by more than a schottky diode for- ward voltage. when using this connection, connect a schottky diode from the battery input to outsu. there is also an internal 10k ? resistance from outsu to insd, which adds a small additional current drain (of approximately (v outsu - v insd )/10k ? from outsu when insd is not connected directly to outsu. step-down direct battery operation improves efficiency for the step-down output (up to 95%), but limits the upper limit of the output voltage to 200mv less than the minimum battery voltage. in 1-cell li+ designs (with a 2.7v min), the output can be set up to 2.5v. in 2-cell alkaline or nimh designs, the output may be limited to 1.5v or 1.8v, depending on the minimum allowed cell voltage. the step-down can only be briefly operated in dropout since the MAX1565 fault protection detects the out-of- regulation condition and activates after 100,000 osc cycles, or 200ms at 500khz. at that point, all MAX1565 channels shut down. auxiliary dc-to-dc controllers the three auxiliary controllers operate as fixed-frequency voltage-mode pwm controllers. they do not have internal mosfets, so output power is determined by external components. the controllers regulate output voltage by modulating the pulse width of the dl_ drive signal to an external n-channel mosfet switch. figure 3 shows a functional diagram of an aux controller channel. a sawtooth oscillator signal at osc governs timing. at the start of each cycle, dl_ goes high, turning on the external n-fet switch. the switch then turns off when the internally level-shifted sawtooth rises above comp_ or when the maximum duty cycle is exceeded. the switch remains off until the start of the next cycle. a transconductance error amplifier forms an integrator at comp_ so that dc high-loop gain and accuracy can be maintained. the auxiliary controllers do not start until the step-up dc-to-dc output is in regulation. if the step-up, step- down, or any of the auxiliary controllers remains faulted for 100,000 osc cycles, then all MAX1565 channels latch off. MAX1565 small, high-efficiency, five-channel digital still camera power supply ______________________________________________________________________________________ 15 r q s clk refi 0.85 ref dl_ fault protection enable level shift ref comp fb osc soft- start* *soft-start ramps refi from 0v to v ref in 4096 clock cycles. figure 3. pwm auxiliary controller functional diagram
MAX1565 maximum duty cycle the MAX1565 auxiliary pwm controllers have a guaran- teed maximum duty cycle of 80%. that is to say that all controllers can achieve at least 80% and typically reach 85%. in boost designs that employ continuous current, the maximum duty cycle limits the boost ratio such that: 1 - v in /v out 80% with discontinuous inductor current, no such limit exists for the input/output ratio since the inductor has time to fully discharge before the next cycle begins. master/slave configurations the MAX1565 supports max1801 slave pwm con- trollers that obtain input power, a voltage reference, and an oscillator signal directly from the MAX1565 master. the master/slave configuration allows channels to be easily added and minimizes system cost by elimi- nating redundant circuitry. the slaves also control the harmonic content of noise since their operating fre- quency is synchronized to that of the MAX1565 master converter. a max1801 connection to the MAX1565 is shown in figure 11. fault protection the MAX1565 has robust fault and overload protection. after power-up, the device is set to detect an out-of regulation state that could be caused by an overload or short. if any dc-to-dc converter channel (step-up, step-down, or any of the auxiliary controllers) remains faulted for 100,000 clock cycles, then all outputs latch off until the step-up dc-to-dc converter is reinitialized by the onsu pin, or by cycling of input power. the fault-detection circuitry for any channel is disabled dur- ing its initial turn-on soft-start sequence. note that output of the step-up, or that of any auxiliary channel set up in boost configuration, does not fall to 0v during shutdown or fault. this is due to the current path from the battery to the output that remains even when the channel is off. this path exists through the boost inductor and the synchronous rectifier body diode. an auxiliary boost channel falls to the input voltage minus the rectifier drop during fault and shutdown. outsu falls to the input voltage minus the synchronous rectifier body diode drop during shutdown, and also during fault if the input voltage exceeds 2.5v. if the input voltage is less than 2.5v, outsu remains at 2.5v due to operation of the startup oscillator, but can source only limited current. reference the MAX1565 has an internal 1.250v reference. connect a 0.1f ceramic bypass capacitor from ref to gnd within 0.2in (5mm) of the ref pin. ref can source up to 200a and is enabled whenever onsd is high and outsd is above 2.5v. the auxiliary controllers and max1801 slave controllers (if connected) each sink up to 30a ref current during startup. if the application requires that ref be loaded beyond 200a, it may be buffered with a unity-gain amplifier or op amp. oscillator all MAX1565 dc-to-dc converter channels employ fixed-frequency pwm operation. the operating fre- quency is set by an rc network at the osc pin. the range of usable settings is 100khz to 1mhz. when max1801 slave controllers are added, they operate at the same frequency set by osc. the oscillator uses a comparator, a 300ns one-shot, and an internal n-fet switch in conjunction with an external timing resistor and capacitor (figure 4). when the switch is open, the capacitor voltage exponentially approaches the step-up output voltage from zero with a time constant given by the r osc c osc product. the comparator output switches high when the capacitor voltage reaches v ref (1.25v). in turn, the one-shot acti- vates the internal mosfet switch to discharge the capacitor within a 300ns interval, and the cycle repeats. note that the oscillation frequency changes as the main output voltage ramps upward following startup. the oscillation f requency is constant once the main output is in regulation. small, high-efficiency, five-channel digital still camera power supply 16 ______________________________________________________________________________________ c osc v ref (1.25v) v outsu r osc osc 300ns one-shot MAX1565 figure 4. master oscillator
low-voltage startup oscillator the MAX1565 internal control and reference-voltage circuitry receive power from outsu and do not function when outsu is less than 2.5v. to ensure low-voltage startup, the step-up employs a low-voltage startup oscillator that activates at 0.9v. the startup oscillator drives the internal n-channel mosfet at lxsu until outsu reaches 2.5v, at which point voltage control is passed to the current-mode pwm circuitry. once in regulation, the MAX1565 operates with inputs as low as 0.7v since internal power for the ic is sup- plied by outsu. at low input voltages, the MAX1565 can have difficulty starting into heavy loads. soft-start the MAX1565 step-down and aux_ channels feature a soft-start function that limits inrush current and prevents excessive battery loading at startup by ramping the output voltage to the regulation voltage. this is achieved by increasing the internal reference inputs to the controller transconductance amplifiers from 0v to the 1.25v reference voltage over 4096 oscillator cycles (8ms at 500khz) when initial power is applied or when a channel is enabled. soft-start is not included in the step-up converter in order to avoid limiting startup capability with loading. shutdown the step-up converter is activated with a high input at onsu. the step-down and auxiliary dc-to-dc convert- ers 1, 2, and 3 activate with a high input at onsd, on1, on2, and on3, respectively. the auxiliary con- trollers and step-down cannot be activated until outsu is in regulation. for automatic startup, connect on_ to outsu or a logic level greater than 1.6v. design procedure setting the switching frequency choose a switching frequency to optimize external component size or circuit efficiency for any particular MAX1565 application. typically, switching frequencies between 300khz and 600khz offer a good balance between component size and circuit efficiency. higher frequencies generally allow smaller components and lower frequencies give better conversion efficiency. the switching frequency is set with an external timing resistor (r osc ) and capacitor (c osc ). at the beginning of a cycle, the timing capacitor charges through the resistor until it reaches v ref . the charge time, t 1 , is: t 1 = -r osc c osc ln [1 - 1.25/v outsu ] the capacitor voltage is then given time (t 2 = 300ns) to discharge. the oscillator frequency is f osc = 1/(t 1 + t 2 ) f osc can operate from 100khz to 1mhz. choose c osc between 47pf and 470pf. determine r osc from the equation: r osc = (300ns - 1/f osc )/(c osc ln [1 - 1.25/v outsu ]) see the typical operating characteristics for f osc versus rosc using different values of cosc. setting output voltages the MAX1565 step-up/step-down converters and the aux1 controllers have both factory-set and adjustable output voltages. these are selected by fbsel_ for the appropriate channel. when fbsel_ is low, the channel output regulates at its preset voltage. when fbsel_ is high, the channel regulates fb_ at 1.25v for use with external feedback resistors. when setting the voltage for auxiliary channels 2 and 3, or when using external feedback at fbsu, fbsd, or fb1, connect a resistive voltage-divider from the output volt- age to the corresponding fb_ input. the fb_ input bias current is less than 100na, so choose the low-side (fb_- to-gnd) resistor (r l ), to be 100k ? or less. then calcu- late the high-side (output-to-fb_) resistor (r h ) using: r h = r l [(v out /1.25) - 1] general filter capacitor selection the input capacitor in a dc-to-dc converter reduces current peaks drawn from the battery, or other input power source, and reduces switching noise in the con- troller. the impedance of the input capacitor at the switching frequency should be less than that of the input source so that high-frequency switching currents do not pass through the input source. MAX1565 small, high-efficiency, five-channel digital still camera power supply ______________________________________________________________________________________ 17 table 1. voltage setting summary channel fb_ fb threshold (fbsel_ low) fb threshold (fbsel_ high) fbsu 3.35v fbsd 1.5v fb1 5v 1.25v fb2 fb2 always 1.25v (fbsel is not provided for these channels)
MAX1565 the output capacitor keeps output ripple small and ensures control-loop stability. the output capacitor must also have low impedance at the switching fre- quency. ceramic, polymer, and tantalum capacitors are suitable, with ceramic exhibiting the lowest esr and high-frequency impedance. output ripple with a ceramic output capacitor is approximately: v ripple = i l(peak) [1/(2 f osc c out )] if the capacitor has significant esr, the output ripple component due to capacitor esr is: v ripple(esr) = i l(peak) esr output capacitor specifics are also discussed in the step-up compensation section and the step-down compensation section. step-up component selection the external components required for the step-up are an inductor, input and output filter capacitor, and com- pensation rc. typically, the inductor is selected to operate with continuous current for best efficiency. an exception might be if the step-up ratio, (v out /v in ), is greater than 1/(1 - d max ), where d max is the maximum pwm duty factor of 80%. when using the step-up channel to boost from a low input voltage, loaded startup is aided by connecting a schottky diode from the battery to outsu. see the minimum startup voltage vs. load current graph in the typical operating characteristics . step-up inductor in most step-up designs, a reasonable inductor value (l ideal ) can be derived from the following equation, which sets continuous peak-to-peak inductor current at one-half the dc inductor current: l ideal = [2 v in(max) d(1 - d)] / (i out f osc ) where d is the duty factor given by: d = 1 - (v in / v out ) given l ideal , the consistent peak-to-peak inductor cur- rent is 0.5 i out /(1 - d). the peak inductor current, i ind(pk) = 1.25 i out / (1 - d). inductance values smaller than l ideal can be used to reduce inductor size. however, if much smaller values are used, the inductor current rises and a larger output capacitance may be required to suppress output ripple. step-up compensation the inductor and output capacitor are usually chosen first in consideration of performance, size, and cost. the compensation resistor and capacitor are then chosen to optimize control-loop stability. in some cases it may help to readjust the inductor or output capacitor value to get optimum results. for typical designs, the component values in the circuit of figure 1 yield good results. the step-up converter employs current-mode control, thereby simplifying the control-loop compensation. when the converter operates with continuous inductor current (typically the case), a right-half-plane zero (rhpz) appears in the loop-gain frequency response. to ensure stability, the control-loop gain should crossover (drop below unity gain) at a frequency (f c ) much less than that of the right-half-plane zero. the relevant characteristics for step-up channel com- pensation are: 1) transconductance (from fbsu to compsu), gm ea (135s) 2) current-sense amplifier transresistance, r cs , (0.3v/a) 3) feedback regulation voltage, v fb (1.25v) 4) step-up output voltage, v suout , in v 5) output load equivalent resistance, r load , in ? = v suout /i load the key steps for step-up compensation are: 1) place f c sufficiently below the rhpz and calculate c c . 2) select r c based on the allowed load-step tran- sient. r c sets a voltage delta on the comp pin that corresponds to load current step. 3) calculate the output filter capacitor (c out ) required to allow the r c and c c selected. 4) determine if c p is required (if calculated to be > 10pf). for continuous conduction, the right-plane zero fre- quency (f rhpz ) is given by: f rhpz = v outsu (1 - d) 2 / (2 l i load ) where d = the duty cycle = 1 - (v in /v out ), l is the inductor value, and i load is the maximum output cur- rent. typically target crossover (f c ) for 1/6 the rhpz. for example, if we assume v in = 2v, v out = 3.35v, and i out = 0.5a, then r load = 6.7 ? . if we select l = 3.3h then: f rhpz = 3.35 (2/3.35) 2 / (2 x 4.7 x 10 -6 x 0.5) = 115khz small, high-efficiency, five-channel digital still camera power supply 18 ______________________________________________________________________________________
choose f c = 20khz. calculate c c : c c = (v fb /v out )(r load /r cs )(gm/2 f c )(1 - d) = (1.25/3.35)(6.7/0.3) x (135s/(6.28 x 20khz) (2/3.35) = 5.35nf choose 6.8nf. now select r c such that transient droop requirements are met. for example, if 4% transient droop is allowed, the input to the error amplifier moves 0.04 x 1.25v, or 50mv. the error amp output drives 50mv x 135s, or 6.75a, across r c to provide tran- sient gain. since the current-sense transresistance is 0.3v/a, the value of r c that allows the required load step swing: r c = 0.3 i ind(pk)/ 6.75a in a step-up dc-to-dc converter, if l ideal is used, out- put current relates to inductor current by: i ind(pk) = 1.25 i out /(1 - d) = 1.25 i out v out /v in thus, for a 400ma output load step with v in = 2v and v out = 3.35v: r c = [1.25(0.3 x 0.4 x 3.35)/2)]/6.75a = 37k ? note that the inductor does not limit the response in this case since it can ramp at 2v/3.3h, or 606ma/s. the output filter capacitor is then chosen so that the c out r load pole cancels the r c c c zero: c out r load = r c c c for example: c out = 37k ? x 6.8nf/6.7 = 37.5f since a reasonable value for c out is 47f rather than 37.5, choose 47f and rescale rc: r c = 47f x 6.7/6.8nf = 46.3k ? which provides a slightly higher transient gain and con- sequently less transient droop than previously selected. if the output filter capacitor has significant esr, a zero occurs at: z esr = 1/(2 c out r esr ) if z esr > f c , it can be ignored, as is typically the case with ceramic output capacitors. if z esr is less than f c , it should be cancelled with a pole set by capacitor c p connected from compsu to gnd: c p = c out r esr /r c if c p is calculated to be < 10pf, it can be omitted. step-down component selection step-down inductor the external components required for the step-down are an inductor, input and output filter capacitors, and compensation rc network. the MAX1565 step-down converter provides best efficiency with continuous inductor current. a reasonable inductor value (lideal) can be derived from: l ideal = 2 (v in ) d (1 - d)/(i out f osc ) which sets the peak-to-peak inductor current at 1/2 the dc inductor current. d is the duty cycle: d = v out /v in given l ideal , the peak-to-peak inductor current varia- tion is 0.5 i out . the absolute peak inductor current is 1.25 i out . inductance values smaller than l ideal can be used to reduce inductor size. however, if much smaller values are used, inductor current rises and a larger output capacitance may be required to suppress output ripple. larger values than l ideal can be used to obtain higher output current, but with typically larger inductor size. step-down compensation the relevant characteristics for step-down compensa- tion are: 1) transconductance (from fbsd to compsd), gm ea (135s) 2) step-down slope compensation pole, p slope = v in /( l) 3) current-sense amplifier transresistance, r cs , (0.6v/a) 4) feedback regulation voltage, v fb (1.25v) 5) step-down output voltage, v sd , in v 6) output load equivalent resistance, r load , in ? = v outsd /i load the key steps for step-down compensation are: 1) set the compensation rc zero to cancel the r load c out pole. 2) set the loop crossover below the lower of 1/5 the slope compensation pole, or 1/5 the switching fre- quency. if we assume v in = 3.35v, v out = 1.5v, and i out = 350ma, then r load = 4.3 ? . MAX1565 small, high-efficiency, five-channel digital still camera power supply ______________________________________________________________________________________ 19
MAX1565 if we select l = 4.7h and f osc = 440khz, p slope = v in /( l) = 214khz, so choose f c = 40khz and calculate c c : c c = (v fb /v out )(r load /r cs )(gm/2 f c ) = (1.25/1.5)(4.3/0.6) x (135s/(6.28 x 40khz) = 3.2nf choose 3.3nf. now select r c such that transient droop requirements are met. for example, if 4% transient droop is allowed, the input to the error amplifier moves 0.04 x 1.25v, or 50mv. the error amp output drives 50mv x 135s, or 6.75a across r c to provide tran- sient gain. since the current-sense transresistance is 0.6v/a, the value of r c that allows the required load step swing: r c = 0.6 i ind(pk) /6.75a in a step-down dc-to-dc converter, if l ideal is used, output current relates to inductor current by: i ind(pk) = 1.25 i out thus, for a 250ma output load step with v in = 3.35v and v out = 1.5v: r c = (1.25 x 0.6 x 0.25)/6.75a = 27.8k ? choose 27k ? . note that the inductor does not limit the response in this case since it can ramp at (v in - v out )/4.7h, or (3.35 - 1.5)/4.7h = 394ma/s. the output filter capacitor is then chosen so that the c out r load pole cancels the r c c c zero: c out r load = r c c c for example: c out = 27k ? x 3.3nf/4.3 = 20.7f choose 22f. if the output filter capacitor has signifi- cant esr, a zero occurs at: z esr = 1/(2 c out r esr ) if z esr > f c , it can be ignored, as is typically the case with ceramic output capacitors. if z esr is less than f c , it should be cancelled with a pole set by capacitor c p connected from compsd to gnd: c p = c out r esr /r c if c p is calculated to be < 10pf, it can be omitted. auxiliary controller component selection external mosfet all MAX1565 auxiliary controllers drive external logic- level n-channel mosfets. significant mosfet selec- tion parameters are: 1) on-resistance (r ds(on) ) 2) maximum drain-to-source voltage (vds(max)) 3) total gate charge (q g ) 4) reverse transfer capacitance (crss) dl_ swings between outsu and gnd. use a mosfet with on-resistance specified at or below the main output voltage. the gate charge, q g , includes all capacitance associated with charging the gate and helps to predict mosfet transition time between on and off states. mosfet power dissipation is a combination of on-resistance and transition losses. the on-resistance loss is: p rdson = d i l 2 r ds(on) where d is the duty cycle, i l is the average inductor current, and r ds(on) is mosfet on-resistance. the transition loss is approximately: p trans = (v out i l f osc t t )/3 where v out is the output voltage, i l is the average inductor current, f osc is the switching frequency, and t t is the transition time. the transition time is approxi- mately q g /i g , where q g is the total gate charge, and i g is the gate drive current (typically 0.5a). the total power dissipation in the mosfet is: p mosfet = p rdson + p trans diode for most auxiliary applications, a schottky diode rectifies the output voltage. the schottky diode s low forward volt- age and fast recovery time provide the best performance in most applications. silicon signal diodes (such as 1n4148) are sometimes adequate in low-current (<10ma) high-voltage (>10v) output circuits where the output voltage is large compared to the diode forward voltage. auxiliary compensation the auxiliary controllers employ voltage-mode control to regulate their output voltage. optimum compensa- tion somewhat depends on whether the design uses continuous or discontinuous inductor current. small, high-efficiency, five-channel digital still camera power supply 20 ______________________________________________________________________________________
discontinuous inductor current when the inductor current falls to zero on each switching cycle, it is described as discontinuous. the inductor is not utilized as efficiently as with continuous current. this often has little negative impact in light-load applications since the coil losses may already be low compared to other losses. a benefit of discontinuous inductor cur- rent is more flexible loop compensation and no maxi- mum duty-cycle restriction on boost ratio. to ensure discontinuous operation, the inductor must have a sufficiently low inductance to fully discharge on each cycle. this occurs when: l < [v in 2 (v out - v in )/v out 3 ] [r load /(2 f osc )] a discontinuous current boost has a single pole at: f p = (2v out - v in )/(2 r load c out v out ) choose the integrator capacitor such that the unity-gain crossover (f c ) occurs at f osc /10 or lower. note that for many auxiliary circuits, such as those powering motors, leds, or other loads that do not require fast transient response, it is often acceptable to overcompensate by setting f c at f osc /20 or lower. c c is then determined by: c c = [2v out v in /((2v out - v in )v ramp )] [v out /(k(v out - v in ))] 1/2 [(v fb /v out ) (g m /(2 f c ))] where k = 2 l f osc /r load, and v ramp is the internal slope compensation voltage ramp of 1.25v. the c c r c zero is then used to cancel the f p pole, so: r c = r load c out v out /[(2v out - v in ) c c ] continuous inductor current continuous inductor current can sometimes improve boost efficiency by lowering the ratio between peak inductor current and output current. it does this at the expense of a larger inductance value that requires larger size for a given current rating. with continuous inductor current boost operation, there is a right-plane zero at: f rhpz = (1 - d) 2 r load /(2 l) where (1 - d) = v in /v out (in a boost converter). a com- plex pole pair is located at: f 0 = v out /[2 v in (l c out ) 1/2 ] if the zero due to the output capacitor capacitance and esr is less than 1/10 the right-plane zero: z cout = 1/(2 c out r esr ) < f rhpz /10 choose c c such that the crossover frequency f c occurs at z cout . the esr zero provides a phase boost at crossover. c c = (v in /v ramp )(v fb /v out )(g m /(2 z cout )) choose r c to place the integrator zero, 1/(2 r c c c ), at f 0 to cancel one of the pole pairs: r c = v in (l c out ) 1/2 /(v out c c ) if z cout is not less than f rhpz /10 (as is typical with ceramic output capacitors) and continuous conduction is required, then cross the loop over before f rhpz and f 0 : f c < f 0 /10, and f c < f rhpz /10 in that case: c c = (v in /v ramp )(v fb /v out )(g m /(2 f c )) place 1/(2 r c c c ) = 1/(2 r load c out ), so that r c = r load c out /c c or reduce the inductor value for dis- continuous operation. applications information led, lcd, and other boost applications any auxiliary channel can be used for a wide variety of step-up applications. these include generating 5v or some other voltage for motor or actuator drive, generating 15v or a similar voltage for lcd bias, or generating a step-up current source to efficiently drive a series array of white leds for display backlighting. figures 5 and 6 show examples of these applications. MAX1565 small, high-efficiency, five-channel digital still camera power supply ______________________________________________________________________________________ 21 MAX1565 (partial) aux_ pwm outsu dl_ fb_ 4.7 h to v batt 4.7 f 22 f 15v 100ma 1.1m ? 100k ? figure 5. using an aux_ controller channel to generate lcd bias
MAX1565 sepic buck-boost the MAX1565 s internal switch step-up and step-down can be cascaded to make a high-efficiency buck-boost converter, but it may sometimes be desirable to build a second buck-boost converter with an aux_ controller. one type of step-up/step-down converter is the sepic (figure 7). inductors l1 and l2 can be separate induc- tors or wound on a single core and coupled like a transformer. typically, a coupled inductor improves efficiency since some power is transferred through the coupling, causing less power to pass through the cou- pling capacitor (c2). likewise, c2 should have low esr to improve efficiency. the ripple current rating must be greater than the larger of the input and output currents. the mosfet (q1) drain-to-source voltage rating, and the rectifier (d1) reverse-voltage rating must exceed the sum of the input and output voltages. other types of step-up/step-down circuits are a flyback converter and a step-up converter followed by a linear regulator. multiple output flyback circuits some applications require multiple voltages from a single converter channel. this is often the case when generating voltages for ccd bias or lcd power. figure 8 shows a two-output flyback configuration with aux_. the controller drives an external mosfet that switches the transformer primary. two transformer secondaries generate the output voltages. only one positive output voltage can be fed back, so the other voltages are set by the turns ratio of the transformer secondaries. the load stability of the other secondary voltages depends on transformer leakage inductance and winding resis- tance. voltage regulation is best when the load on the secondary that is not fed back is small when compared to the load on the one that is. regulation also improves if the load current range is limited. consult the trans- former manufacturer for the proper design for a given application. boost with charge pump for positive and negative outputs negative output voltages can be produced without a transformer, using a charge-pump circuit with an auxil- iary controller as shown in figure 9. when mosfet q1 turns off, the voltage at its drain rises to supply current to v out +. at the same time, c1 charges to the voltage v out + through d1. small, high-efficiency, five-channel digital still camera power supply 22 ______________________________________________________________________________________ MAX1565 (partial) aux_ pwm outsu dl_ fb_ 10 h to v batt 1 f 1 f 62 ? (for 20ma) white leds figure 6. aux_ channel powering a white led step-up current source q 1 c 2 d 1 r 1 output 3.3v l 1 r 2 main in dcon part of MAX1565 dl fb input 1-cell li+ l 2 figure 7. auxiliary sepic configuration MAX1565 (partial) aux_ pwm outsu dl_ fb_ to v batt 1 f 1 f 1 f +15v 30ma ccd+ -7.5v 20ma ccd- 1.1m ? 100k ? *(see note) *load resistor required if -7.5v operates with no load figure 8. +15v and -7.5v ccd bias with transformer
when the mosfet turns on, c1 discharges through d3, thereby charging c3 to v out - minus the drop across d3 to create roughly the same voltage as v out + at v out - but with inverted polarity. if different magnitudes are required for the positive and negative voltages, a linear regulator can be used at one of the outputs to achieve the desired voltages. one such connection is shown in figure 10. this circuit is somewhat unique in that a positive output linear regula- tor is able to regulate the negative output. it does this by controlling the charge to the flying capacitor rather than directly regulating at the output. adding a max1801 slave the max1801 is a 6-pin sot slave dc-to-dc controller that can be connected to generate additional output voltages. it does not generate its own reference or oscillator. instead, it uses the reference and oscillator of the MAX1565 (figure 11). the max1801 controller operation and design are similar to that of a MAX1565 aux controller. all comments in the auxiliary controller component selection section also apply to add-on max1801 slave controllers. for more details, refer to the max1801 data sheet. MAX1565 small, high-efficiency, five-channel digital still camera power supply ______________________________________________________________________________________ 23 MAX1565 (partial) aux_ pwm outsu dl_ fb_ c2 1 f to v batt 1 f l1 10 h d2 r1 1m ? r2 90.9k ? c1 1 f d3 d1 q1 c3 1 f v out+ +15v 20ma v out- -15v 10ma figure 9. 15v output using a boost with charge-pump inversion MAX1565 (partial) aux_ pwm outsu dl_ fb_ 1 f to v batt 1 f 10 h 1m ? 90.9k ? 1 f q1 1 f 1 f 110k ? 549k ? max1616 fb_ gnd shdn in out +1.25v +15v 20ma -7.5v 20ma figure 10. +15v and -7.5v ccd bias without transformer
MAX1565 using sdok for power sequencing sdok goes low when the step-down reaches regula- tion. some microcontrollers with low-voltage cores require that the high-voltage (3.3v) i/o rail not be powered up until the core has a valid supply. the circuit in figure 12 accomplishes this by driving the gate of a pfet connected between the 3.3v output and the microcontroller i/o supply. alternately, power sequencing may be implemented by connecting rc networks to the appropriate converter on_ inputs. setting outsd below 1.25v the step-down feedback voltage is 1.25v when fbselsd is high. with a standard two-resistor feed- back network, the output voltage may be set to values between 1.25v and the input voltage. if a step-down output voltage less than 1.25v is desired, it can be set by adding a third feedback resistor from fb to a voltage higher than 1.25v (the step-up output is a convenient voltage for this) as shown in figure 13. the equation governing output voltage shown in figure 13 is: 0 = [(v sd - v fbsd )/r1] + [(0 - v fbsd )/r2] + [(v su - v fbsd )/r3] where v sd is the output voltage, v fbsd is 1.25v, and v su is the step-up output voltage. note that any avail- able voltage that is higher than 1.25v can be used as the connection point for r3 in figure 13 and for the v sd term in the equation. since there are multiple solutions for r1, r2, and r3, the above equation cannot be writ- ten in terms of one resistor. the best method for deter- mining resistor values is to enter the above equation into a spreadsheet and test estimated resistors values. a good starting point is with 100k ? at r2 and r3. small, high-efficiency, five-channel digital still camera power supply 24 ______________________________________________________________________________________ MAX1565 (partial) max1801 to batt dl fb comp gnd ref osc in dcon outsu osc ref v out figure 11. connecting the max1801 slave pwm controller to the MAX1565 step-up step-down MAX1565 (partial) outsub outsua lxsu pgndb fbsu sdok insd lxsd fbsd 10 h 4.7 h 10 f 10 f 1 0 f to vbatt 1m ? 1m ? 3.35v 3.3v to cpu v core 1.5v to v batt or outsu pgnda figure 12. using sdok to gate 3.3v power to cpu after the core voltage is ok
designing a pc board good pc board layout is important to achieve optimal performance from the MAX1565. poor design can cause excessive conducted and/or radiated noise. conductors carrying discontinuous currents, and any high-current path should be made as short and wide as possible. a separate low-noise ground plane containing the reference and signal grounds should connect to the power-ground plane at only one point to minimize the effects of power-ground currents. typically, the ground planes are best joined right at the ic. keep the voltage feedback network very close to the ic, preferably within 0.2in (5mm) of the fb_ pin. nodes with high dv/dt (switching nodes) should be kept as small as possible and should be routed away from high-impedance nodes such as fb_. refer to the MAX1565evkit evaluation kit data sheet for a full pc board example. chip information transistor count: 9420 process: bicmos MAX1565 small, high-efficiency, five-channel digital still camera power supply ______________________________________________________________________________________ 25 current-mode step-down insd lxsd 4.7 h 22 f 10 f pgnda MAX1565 (partial) outsua outsub fbselsd r1 56k ? r3 100k ? r2 100k ? fbsd v fbsd 1.25v v su 3.3v v sd 0.8v figure 13. setting outsd for outputs below 1.25v
MAX1565 small, high-efficiency, five-channel digital still camera power supply maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 26 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2003 maxim integrated products printed usa is a registered trademark of maxim integrated products. qfn thin.eps d2 (nd-1) x e e d c pin # 1 i.d. (ne-1) x e e/2 e 0.08 c 0.10 c a a1 a3 detail a 0.15 c b 0.15 c a document control no. 21-0140 package outline 16, 20, 28, 32l, qfn thin, 5x5x0.8 mm proprietary information approval title: c rev. 2 1 e2/2 e2 0.10 m c a b pin # 1 i.d. b 0.35x45 l d/2 d2/2 l c l c e e l cc l k k l l 2 2 21-0140 rev. document control no. approval proprietary information title: common dimensions exposed pad variations 1. dimensioning & tolerancing conform to asme y14.5m-1994. 2. all dimensions are in millimeters. angles are in degrees. 3. n is the total number of terminals. 4. the terminal #1 identifier and terminal numbering convention shall conform to jesd 95-1 spp-012. details of terminal #1 identifier are optional, but must be located within the zone indicated. the terminal #1 identifier may be either a mold or marked feature. 5. dimension b applies to metallized terminal and is measured between 0.25 mm and 0.30 mm from terminal tip. 6. nd and ne refer to the number of terminals on each d and e side respectively. 7. depopulation is possible in a symmetrical fashion. 8. coplanarity applies to the exposed heat sink slug as well as the terminals. 9. drawing conforms to jedec mo220. notes: 10. warpage shall not exceed 0.10 mm. c package outline 16, 20, 28, 32l, qfn thin, 5x5x0.8 mm package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline information, go to www.maxim-ic.com/packages .)

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