View LTC8606_9008603.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

1 for more information www.linear.com/lt8606 features typical application description 42v, 350ma synchronous step-down regulator with 2.5a quiescent current the lt ? 8606 is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator that consumes only 1.7a of non-switching quiescent current. the lt8606 can deliver 350ma of continuous current. top and bottom power switches are included with all necessary circuitry to minimize the need for external components. low ripple burst mode operation enables high efficiency down to very low output currents while keeping the output ripple below 10mv p-p . internal com- pensation with peak current mode topology allows the use of small inductors and results in fast transient response and good loop stability. the en/uv pin has an accurate 1v threshold and can be used to program v in undervoltage lockout or to shut down the lt8606 reducing the input supply current to 1a. the pg pin signals when v out is within 8.5% of the programmed output voltage as well as fault conditions. the msop package includes a sync pin to synchronize to an external clock, or to select burst mode operation or pulse-skipping with or without spread-spectrum; the tr/ss pin programs soft-start or tracking. applications n wide input voltage range: 3.0v to 42v n ultralow quiescent current burst mode ? operation: n <3a i q regulating 12v in to 3.3v out n output ripple <10mv p-p n high effciency 2mhz synchronous operation: n >92% efficiency at 0.35a, 12v in to 5v out n 350ma maximum continuous output n fast minimum switch-on time: 35ns n adjustable and synchronizable: 200khz to 2.2mhz n spread spectrum frequency modulation for low emi n allows use of small inductors n low dropout n peak current mode operation n accurate 1v enable pin threshold n internal compensation n output soft-start and tracking n small thermally enhanced 10-lead msop package or 8-pin 2mm 2mm dfn package n general purpose step-down converter n low emi step down all registered trademarks and trademarks are the property of their respective owners. 5v, 2mhz step-down 12v in to 5v out efficiency 0 0 6 0 0 8 8606 0 0 8606 00 8 000 0 080 f lt c8606 8606fb 250 300 350 50 55 60 65 70 75 80 f sw = 2mhz 85 90 95 100 efficiency (%) 8606 ta01b l = 10h i out (ma) 0 50 100 150 200
2 for more information www.linear.com/lt8606 pin configuration absolute maximum ratings v in , en/uv, pg .......................................................... 42 v fb, tr/ss . ................................................................. 4v sync voltage . ............................................................ 6v (note 1) 1 2 3 4 5 bst sw intv cc rt sync 10 9 8 7 6 en/uv v in pg tr/ss fb top view 11 gnd mse package 10-lead plastic msop ja = 40c/w exposed pad (pin 11) is gnd, must be soldered to pcb 8 6 8 ja = 102c/w exposed pad (pin 9) is gnd, must be soldered to pcb order information lead free finish tape and reel part marking* package description temperature range lt8606emse#pbf lt8606emse#trpbf ltgxt 10-lead plastic msop C40c to 125c lt8606imse#pbf lt8606imse#trpbf ltgxt 10-lead plastic msop C40c to 125c lt8606hmse#pbf lt8606hmse#trpbf ltgxt 10-lead plastic msop C40c to 150c lt8606edc#pbf lt8606edc#trpbf lgxv 8-lead plastic 2mm 2mm dfn C40c to 125c lt8606idc#pbf lt8606idc#trpbf lgxv 8-lead plastic 2mm 2mm dfn C40c to 125c lt8606hdc#pbf lt8606hdc#trpbf lgxv 8-lead plastic 2mm 2mm dfn C40c to 150c consult ltc marketing for parts specified with wider operating temperature ranges. *the temperature grade is identified by a label on the shipping container. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. some packages are available in 500 unit reels through designated sales channels with #trmpbf suffix. the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. http://www.linear.com/product/lt8606#orderinfo electrical characteristics operating junction temperature range (note 2) lt 8606 e ............................................ C 40 c to 125 c lt 8606 i ............................................. C 40 c to 125 c lt 8606 h ............................................ C 40 c to 150 c storage temperature range .................. C 65 c to 150 c parameter conditions min typ max units minimum input voltage l 2.5 3.0 3.2 v v in quiescent current v en/uv = 0v v en/uv = 2v, not switching, v sync = 0v or dfn, v in 36v l 1 1.7 5 12 a a v in current in regulation v in = 6v, v out = 2.7v, output load = 100a v in = 6v, v out = 2.7v, output load = 1ma l l 56 500 90 700 a a lt c8606 8606fb
3 for more information www.linear.com/lt8606 the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: the lt8606e is guaranteed to meet performance specifications from 0c to 125c junction temperature. specifications over the C40c to 125c operating junction temperature range are assured by design, characterization, and correlation with statistical process controls. the lt8606i is guaranteed over the full C40c to 125c operating junction temperature range. the lt8606h is guaranteed over the full C40c to 150c operating junction temperature range. high junction temperatures degrade operating lifetimes. operating lifetime is derated at junction temperatures greater than 125c. note 3: this ic includes overtemperature protection that is intended to protect the device during overload conditions. junction temperature will exceed 150c when overtemperature protection is active. continuous operation above the specified maximum operating junction temperature will reduce lifetime. parameter conditions min typ max units feedback reference voltage msop package v in = 6v, i load = 100ma v in = 6v, i load = 100ma l 0.774 0.762 0.778 0.778 0.782 0.798 v v dfn package v in = 6v, i load = 100ma v in = 6v, i load = 100ma l 0.771 0.753 0.778 0.778 0.785 0.803 v v feedback v oltage line regulation v in = 4.0v to 40v l 0.02 0.06 %/v feedback pin input current v fb = 1v 20 na minimum on-time i load = 350ma i load = 350ma, sync = 1.9v l l 35 35 65 60 ns ns minimum off t ime i load = 300ma l 93 130 ns oscillator frequency msop package r t = 221k, i load = 250ma r t = 60.4k, i load = 250ma r t = 18.2k, i load = 250ma l l l 155 640 1.90 200 700 2.00 245 760 2.10 khz khz mhz dfn package r t = 221k, i load = 250ma r t = 60.4k, i load = 250ma r t = 18.2k, i load = 250ma l l l 140 610 1.85 200 700 2.00 260 790 2.15 khz khz mhz t op power nmos on-resistance i load = 250ma 375 m top power nmos current limit msop package l 0.65 0.9 1.15 a dfn package l 0.65 1.1 1.4 a bottom power nmos on-resistance 240 m sw leakage current v in = 36v 5 a en/uv pin threshold en/uv rising l 0.99 1.05 1.11 v en/uv pin hysteresis 50 mv en/uv pin current v en/uv = 2v 20 na pg upper threshold offset from v fb v fb rising l 5.0 8.5 13.0 % pg lower threshold offset from v fb v fb falling l 5.0 8.5 13.0 % pg hysteresis 0.5 % pg leakage v pg = 42v 200 na pg pull-down resistance v pg = 0.1v 550 1200 sync low input voltage msop only l 0.4 0.9 v sync high input voltage intv cc = 3.5v, msop only l 2.7 3.2 v tr/ss source current msop only l 1 2 3 a tr/ss pull-down resistance fault condition, tr/ss = 0.1v, msop only 300 900 spread spectrum modulation frequency v sync = 3.3v, msop only 0.5 3 6 khz electrical characteristics lt c8606 8606fb
4 for more information www.linear.com/lt8606 fb voltage load regulation efficiency (3.3v output, burst mode operation) typical performance characteristics efficiency (5v output, burst mode operation) efficiency (5v output, burst mode operation) efficiency (3.3v output, burst mode operation) v in = 12v v in = 24v v in = 12v v in = 24v v in = 12v v in = 24v v in = 12v v in = 24v t a = 25c, unless otherwise noted. lt c8606 8606fb 350 776 777 778 779 780 fb regulation voltage (mv) 8606 g05 output current (ma) 0 50 50 100 150 200 250 300 350 ?0.20 ?0.15 ?0.10 ?0.05 55 0.00 0.05 0.10 0.15 0.20 change in v out (%) 8606 g06 60 65 70 75 80 85 90 i out (ma) 95 100 efficiency (%) 8606 g01 l = 10h f sw = 2mhz i out (ma) 0.001 0.01 0.1 1 0 10 100 500 0 10 20 30 40 50 60 50 70 80 90 100 efficiency (%) 8606 g02 l = 10h f sw = 2mhz i out (ma) 0 50 100 100 150 200 250 300 350 50 55 60 65 150 70 75 80 85 90 95 100 efficiency (%) 8606 g03 l = 6.8h f sw = 2mhz 200 i out (ma) 0.001 0.01 0.1 1 10 100 500 0 10 250 20 30 40 50 60 70 80 90 100 efficiency (%) 300 8606 g04 l = 6.8h f sw = 2mhz temperature (c) ?50 ?10 30 70 110 150 775
5 for more information www.linear.com/lt8606 typical performance characteristics line regulation no-load supply current (3.3v output switching) no-load supply current vs temperature (not switching) top fet current limit vs duty cycle top fet current limit vs temperature switch drop vs temperature switch drop vs switch current top sw bot sw top sw bot sw t a = 25c, unless otherwise noted. lt c8606 8606fb ?0.15 90 110 130 150 0 50 100 150 200 250 ?0.10 switch drop (mv) 8606 g12 switch current (ma) 0 50 100 150 200 250 300 ?0.05 350 0 25 50 75 100 125 150 175 200 0.00 switch drop (mv) 8606 g13 0.05 0.10 0.15 0.20 change in v out (%) 8606 g07 input voltage (v) l = 10h input voltage (v) 2 10 18 26 34 42 2.00 2.25 2 2.50 2.75 3.00 3.25 3.50 3.75 4.00 4.25 4.50 i in (a) 10 8606 g08 temperature (c) ?50 ?10 30 70 110 150 1.3 1.5 18 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 3.3 input current (a) 26 8606 g09 duty cycle (%) 0 20 40 60 80 100 0.60 0.70 34 0.80 0.90 1.00 1.10 top fet current limit (a) 8606 g10 duty cycle = 0 temperature (c) ?50 ?10 42 30 70 110 150 0.90 0.95 1.00 1.05 1.10 top fet current limit (a) ?0.20 8606 g11 switch current = 350ma temperature (c) ?50 ?30 ?10 10 30 50 70
6 for more information www.linear.com/lt8606 typical performance characteristics t a = 25c, unless otherwise noted. minimum on-time vs temperature minimum off-time vs temperature dropout voltage vs output current switching frequency vs temperature burst frequency vs output current minimum load to full frequency (sync float to 1.9v) (msop package) lt c8606 8606fb 70 1000 1250 1500 1750 2000 2250 2500 switching frequency (khz) 8606 g18 l = 6.8h v in = 12v v out = 3.3v sync = 0v 90 l = 10h v in = 12v v out = 5v r t = 18.2k input voltage (v) 0 5 10 15 20 25 30 35 110 40 45 0 5 10 15 20 output current (ma) 8606 g19 130 150 30 31 32 33 34 i out = 350ma 35 36 37 38 39 40 minimum on?time (ns) 8606 g14 i out = 300ma temperature (c) temperature (c) ?50 ?30 ?10 10 30 50 70 90 110 130 ?50 150 80 85 90 95 100 105 110 minimum off?time (ns) 8606 g15 ?30 l = xfl3010?682me 0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0 ?10 50 100 150 200 250 dropout voltage (mv) 8606 g16 output current (a) r t = 18.2k temperature (c) 10 ?50 ?10 30 70 110 150 1975 1980 1985 1990 30 1995 2000 2005 2010 2015 2020 2025 switching frequency (khz) 8606 g17 output current (ma) 50 0 25 50 75 100 125 0 250 500 750
7 for more information www.linear.com/lt8606 typical performance characteristics t a = 25c, unless otherwise noted. frequency foldback soft-start tracking (msop package) soft-start current vs temperature (msop package) v in uvlo start-up dropout start-up dropout sync = 0v r t = 18.2k v in v out v in v out lt c8606 8606fb 0.7 1 2 3 4 5 6 7 0 1 2 0.8 3 4 5 6 7 0 1 2 3 4 0.9 5 6 7 input voltage (v) output voltage (v) 8606 g24 r load = 15 input voltage (v) 0 1 1.0 2 3 4 5 6 7 0 1 2 3 0 4 5 6 7 0 1 2 3 4 5 250 6 7 input voltage (v) output voltage (v) 8606 g25 500 750 1000 1250 fb voltage (v) 1500 1750 2000 2250 2500 frequency (khz) 8606 g20 ss voltage (v) 0 0.1 0.0 0.2 0.4 0.5 0.6 0.7 0.8 1.0 1.1 1.2 0 0.1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.2 fb voltage (v) 8606 g21 temperature (c) ?50 ?30 ?10 10 30 50 70 0.3 90 110 130 150 1.5 1.6 1.7 1.8 1.9 2.0 0.4 2.1 2.2 2.3 2.4 2.5 soft start current (a) 8606 g22 temperature (c) ?50 ?30 0.5 ?10 10 30 50 70 90 110 130 150 2.00 0.6 2.25 2.50 2.75 3.00 3.25 v in uvlo (v) 8606 g23 r load = 50 input voltage (v) 0
8 for more information www.linear.com/lt8606 typical performance characteristics transient response transient response switching waveforms switching waveforms switching waveforms 200ns/div v sw 5v/div i load 100ma/div 8606 g26 12v in to 5v out at 250ma 2mhz 200ns/div v sw 10v/div i load 100ma/div 8606 g27 36v in to 5v out at 250ma 2mhz 2s/div sw 5v/div i load 100ma/div v out 20mv/div 8606 g28 12v in to 5v out at 5ma 10f c out 200s/div v out 100mv/div i load 100ma/div 8606 g29 v in =12v, v out = 5v 25ma to 275ma c out = 22f f sw = 2mhz 200s/div v out 100mv/div i load 100ma/div 8606 g30 v in =12v, v out = 5v 100ma to 350ma c out = 22f f sw = 2mhz t a = 25c, unless otherwise noted. frequency (mhz) amplitude (dbv) 50 ?5 40 25 15 5 30 45 35 20 10 0 ?10 8606 g31 0 500 900 300 700 1000 400 800 200 600 100 vertical polarization peak detector class 5 peak limit spread spectrum mode fixed frequency dc2564a demo board with emi filter installed 14v input to 5v output at 350ma, f sw = 2mhz radiated emi performance (cispr25 radiated emission test with class 5 peak limits) lt c8606 8606fb
9 for more information www.linear.com/lt8606 pin functions bst: this pin is used to provide a drive voltage, higher than the input voltage, to the topside power switch. place a 0.1f boost capacitor as close as possible to the ic. do not place a resistor in series with this pin. sw : the sw pin is the output of the internal power switches. connect this pin to the inductor and boost capacitor. this node should be kept small on the pcb for good performance. intv cc internal 3.5v regulator bypass pin. the internal power drivers and control circuits are powered from this voltage. intv cc max output current is 20ma . voltage on intv cc will vary between 2.8v and 3.5v . decouple this pin to power ground with at least a 1f low esr ceramic capacitor. do not load the intv cc pin with exter - nal circuitry. rt : a resistor is tied between rt and ground to set the switching frequency. when synchronizing, the r t resistor should be chosen to set the lt8606 switching frequency to equal or below the lowest synchronization input. sync (msop only): external clock synchronization input. ground this pin for low ripple burst mode operation at low output loads. tie to a clock source for synchroni - zation to an external frequency. leave floating for pulse- skipping mode with no spread spectrum modulation. t ie to intv cc or tie to a voltage between 3.2v and 5.0v for pulse-skipping mode with spread spectrum modulation. when in pulse-skipping mode, the i q regulating no load will increase to several ma. there is no sync pin on the lt8606 dfn and the node is internally tied to ground. fb: the lt8606 regulates the fb pin to 0.778v . connect the feedback resistor divider tap to this pin. tr/ss (msop only): output tracking and soft-start pin. this pin allows user control of output voltage ramp rate during start-up. a tr/ss voltage below 0.778v forces the lt8606 to regulate the fb pin to equal the tr/ss pin volt - age. when tr/ss is above 0.778v, the tracking function is disabled and the internal reference resumes control of the error amplifier. an internal 2a pull-up current from intv cc on this pin allows a capacitor to program out - put voltage slew rate. this pin is pulled to ground with a 300 mosfet during shutdown and fault conditions; use a series resistor if driving from a low impedance output. there is no tr/ss pin on the lt8606 dfn and the node is internally floated. pg: the pg pin is the open-drain output of an internal comparator. pg remains low until the fb pin is within 8.5% of the final regulation voltage, and there are no fault conditions. pg is valid when v in is above 3.2v and when en/uv is high. pg is pulled low when v in is above 3.2v and en/uv is low. if v in is near zero, pg will be high impedance. v in : the v in pin supplies current to the lt8606 internal circuitry and to the internal topside power switch. this pin must be locally bypassed. be sure to place the positive terminal of the input capacitor as close as possible to the v in pins, and the negative capacitor terminal as close as possible to the gnd pins. en/uv: the lt8606 is shut down when this pin is low and active when this pin is high. the hysteretic threshold volt - age is 1.05v going up and 1.00v going down. tie to v in if the shutdown feature is not used. an external resistor divider from v in can be used to program a v in threshold below which the lt8606 will shut down. gnd: exposed pad pin. the exposed pad must be con - nected to the negative terminal of the input capacitor and soldered to the pcb in order to lower the thermal resistance. lt c8606 8606fb
10 for more information www.linear.com/lt8606 block diagram + + ? + ? slope comp internal 0.778v ref oscillator 200khz to 2.2mhz burst detect 3.5v reg m1 m2 c bst c out v out 8606 bd sw l bst switch logic and anti- shoot through error amp shdn 8.5% v c shdn tsd intv cc uvlo v in uvlo shdn tsd v in uvlo en/uv 1v + ? intv cc gnd pg fb r1 r pg r2 r t c ss v out c ff tr/ss (msop only) 2a rt sync (msop only) v in v in c in c vcc r3 opt r4 opt lt c8606 8606fb
11 for more information www.linear.com/lt8606 operation the lt8606 is a monolithic constant frequency current mode step-down dc/dc converter. an oscillator with frequency set using a resistor on the rt pin turns on the internal top power switch at the beginning of each clock cycle. current in the inductor then increases until the top switch current comparator trips and turns off the top power switch. the peak inductor current at which the top switch turns off is controlled by the voltage on the internal vc node. the error amplifier servos the vc node by comparing the voltage on the v fb pin with an inter - nal 0.778v reference. when the load current increases it causes a reduction in the feedback voltage relative to the reference leading the error amplifier to raise the vc volt - age until the average inductor current matches the new load current. when the top power switch turns off the synchronous power switch turns on until the next clock cycle begins or inductor current falls to zero. if overload conditions result in excess current flowing through the bottom switch, the next clock cycle will be delayed until switch current returns to a safe level. if the en/uv pin is low, the lt8606 is shut down and draws 1a from the input. when the en/uv pin is above 1.05v, the switching regulator becomes active. to optimize efficiency at light loads, the lt8606 enters burst mode operation during light load situations. between bursts, all circuitry associated with controlling the output switch is shut down, reducing the input supply current to 1.7a. in a typical application, 3.0a will be consumed from the input supply when regulating with no load. the sync pin is tied low to use burst mode operation and can be floated to use pulse-skipping mode. if a clock is applied to the sync pin the part will synchronize to an external clock frequency and operate in pulse-skipping mode. while in pulse-skipping mode the oscillator oper - ates continuously and positive sw transitions are aligned to the clock. during light loads, switch pulses are skipped to regulate the output and the quiescent current will be several ma. the sync pin may be tied high for spread spectrum modulation mode, and the lt8606 will operate similar to pulse-skipping mode but vary the clock fre - quency to reduce emi. the lt8606 dfn has no sync pin and will always operate in burst mode operation. comparators monitoring the fb pin voltage will pull the pg pin low if the output voltage varies more than 8.5% (typi - cal) from the set point, or if a fault condition is present. the oscillator reduces the lt8606 s operating frequency when the voltage at the fb pin is low and the part is in burst mode operation. this frequency foldback helps to control the inductor current when the output voltage is lower than the programmed value which occurs during start-up. lt c8606 8606fb
12 for more information www.linear.com/lt8606 applications information achieving ultralow quiescent current to enhance efficiency at light loads, the lt8606 enters into low ripple burst mode operation, which keeps the output capacitor charged to the desired output voltage while minimizing the input quiescent current and mini - mizing output voltage ripple. in burst mode operation the lt8606 delivers single small pulses of current to the out - put capacitor followed by sleep periods where the output power is supplied by the output capacitor . while in sleep mode the lt8606 consumes 1.7a. as the output load decreases, the frequency of single cur - rent pulses decreases (see figure 1) and the percentage of time the lt8606 is in sleep mode increases, result - ing in much higher light load efficiency than for typical converters. by maximizing the time between pulses, the converter quiescent current approaches 3.0a for a typi - cal application when there is no output load. therefore, to optimize the quiescent current performance at light loads, the current in the feedback resistor divider must be minimized as it appears to the output as load current. while in burst mode operation the current limit of the top switch is approximately 150ma resulting in output voltage ripple shown in figure 3. increasing the output capacitance will decrease the output ripple proportionally. as load ramps upward from zero the switching frequency will increase but only up to the switching frequency pro- grammed by the resistor at the rt pin as shown in table 1. the output load at which the lt8606 reaches the pro - grammed frequency varies based on input voltage, output voltage, and inductor choice. for some applications it is desirable for the lt8606 to operate in pulse-skipping mode, offering two major differ - ences from burst mode operation. first is the clock stays awake at all times and all switching cycles are aligned to the clock. in this mode much of the internal circuitry is awake at all times, increasing quiescent current to several hundred a. second is that full switching frequency is reached at lower output load than in burst mode operation as shown in figure 2. to enable pulse-skipping mode the sync pin is floated. to achieve spread spectrum modula - tion with pulse-skipping mode, the sync pin is tied high. while a clock is applied to the sync pin the lt8606 will figure 2. full switching frequency minimum load vs v in in pulse skipping mode (msop only) figure 3. burst mode operation figure 1. sw burst mode frequency vs output current 2s/div sw 5v/div i load 100ma/div v out 20mv/div 8606 f03 also operate in pulse-skipping mode. the lt8606 dfn is always programmed for burst mode operation and cannot enter pulse-skipping mode. lt c8606 8606fb 500 750 1000 1250 1500 1750 2000 2250 2500 switching frequency (khz) 0 8606 f01 l = 6.8h v in = 12v v out = 3.3v sync = 0v output current (ma) input voltage (v) 0 5 10 15 20 25 25 30 35 40 45 0 5 10 15 20 output current (ma) 50 8606 f02 l = 10h v in = 12v v out = 5v r t = 18.2k 75 100 125 0 250
13 for more information www.linear.com/lt8606 applications information fb resistor network the output voltage is programmed with a resistor divider between the output and the fb pin. choose the resistor values according to: r1 = r2 v out 0.778v ? 1 ? ? ? ? ? ? 1% resistors are recommended to maintain output volt - age accuracy. the total resistance of the fb resistor divider should be selected to be as large as possible when good low load efficiency is desired: the resistor divider generates a small load on the output, which should be minimized to optimize the quiescent current at low loads. when using large fb resistors, a 10pf phase lead capaci - tor should be connected from v out to fb. setting the switching frequency the lt8606 uses a constant frequency pwm architec - ture that can be programmed to switch from 200khz to 2.2mhz by using a resistor tied from the rt pin to ground. a table showing the necessary r t value for a desired switching frequency is in table 1. when in spread spectrum modulation mode, the frequency is modulated upwards of the frequency set by r t . table 1. sw frequency vs r t value f sw (mhz) r t (k) 0.2 221 0.300 143 0.400 110 0.500 86.6 0.600 71.5 0.700 60.4 0.800 52.3 0.900 46.4 1.000 40.2 1.200 33.2 1.400 27.4 1.600 23.7 1.800 20.5 2.000 18.2 2.200 16.2 operating frequency selection and trade-offs selection of the operating frequency is a trade-off between efficiency, component size, and input voltage range. the advantage of high frequency operation is that smaller inductor and capacitor values may be used. the disad - vantages are lower efficiency and a smaller input voltage range. the highest switching frequency (f sw(max) ) for a given application can be calculated as follows: f sw(max) = v out + v sw(bot) t on(min) v in C v sw(top) + v sw(bot) ( ) = v out + v sw(bot) 1C f sw ? t off(min) C v sw(bot) + v sw(top) where v in(min) is the minimum input voltage without skipped cycles, v out is the output voltage, v sw(top) and v sw(bot) are the internal switch drops ( ~0.13v, ~0.06v, respectively at max load), f sw is the switching frequency (set by r t ), and t off(min) is the minimum switch off- time. note that higher switching frequency will increase the minimum input voltage below which cycles will be dropped to achieve higher duty cycle. lt c8606 8606fb
14 for more information www.linear.com/lt8606 applications information inductor selection and maximum output current the lt8606 is designed to minimize solution size by allowing the inductor to be chosen based on the output load requirements of the application. during overload or short circuit conditions the lt8606 safely tolerates opera - tion with a saturated inductor through the use of a high speed peak-current mode architecture. a good first choice for the inductor value is: l = v out + v sw(bot) f sw ? 4 where f sw is the switching frequency in mhz, v out is the output voltage, v sw(bot) is the bottom switch drop (~0.06v) and l is the inductor value in h. to avoid overheating and poor efficiency, an inductor must be chosen with an rms current rating that is greater than the maximum expected output load of the applica - tion. in addition, the saturation current (typically labeled i sat ) rating of the inductor must be higher than the load current plus 1/2 of in inductor ripple current: i l(peak) = i load(max) + 1 2 l where ? i l is the inductor ripple current as calculated sev - eral paragraphs below and i load(max) is the maximum output load for a given application. as a quick example, an application requiring 0.25a output should use an inductor with an rms rating of greater than 0.5a and an i sat of greater than 0.7a . to keep the efficiency high, the series resistance (dcr) should be less than 0.04 , and the core material should be intended for high frequency applications. the lt8606 limits the peak switch current in order to protect the switches and the system from overload faults. the top switch current limit (i lim ) is at least 0.65a at low duty cycles and decreases linearly to at least 0.5a at d? = ?0.8. the inductor value must then be sufficient to supply the desired maximum output current (i out(max) ), which is a function of the switch current limit (i lim ) and the ripple current: i out(max) = i lim ? i l 2 the peak-to-peak ripple current in the inductor can be calculated as follows: i l = v out l ? f sw 1? v out v in(max) ? ? ? ? ? ? where f sw is the switching frequency of the lt8606, and l is the value of the inductor. therefore, the maximum output current that the lt8606 will deliver depends on the switch current limit, the inductor value, and the input and output voltages. the inductor value may have to be increased if the inductor ripple current does not allow sufficient maximum output current (i out(max) ) given the switching frequency, and maximum input voltage used in the desired application. the optimum inductor for a given application may differ from the one indicated by this design guide. a larger value inductor provides a higher maximum load current and reduces the output voltage ripple. for applications requir - ing smaller load currents, the value of the inductor may be lower and the lt8606 may operate with higher ripple current. this allows use of a physically smaller inductor, or one with a lower dcr resulting in higher efficiency. be aware that low inductance may result in discontinuous mode operation, which further reduces maximum load current. for more information about maximum output current and discontinuous operation, see analog devices application note 44. finally, for duty cycles greater than 50% (v out /v in > 0.5), a minimum inductance is required to avoid sub-harmonic oscillation. see application note 19. input capacitor bypass the input of the lt8606 circuit with a ceramic capacitor of x7r or x5r type. y5v types have poor per - formance over temperature and applied voltage, and should not be used. a 4.7f to 10f ceramic capacitor is adequate to bypass the lt8606 and will easily handle the ripple current. note that larger input capacitance is required when a lower switching frequency is used. if the input power source has high impedance, or there is lt c8606 8606fb
15 for more information www.linear.com/lt8606 applications information significant inductance due to long wires or cables, addi - tional bulk capacitance may be necessary. this can be provided with a low performance electrolytic capacitor. step-down regulators draw current from the input sup - ply in pulses with very fast rise and fall times. the input capacitor is required to reduce the resulting voltage rip - ple at the lt8606 and to force this very high frequency switching current into a tight local loop, minimizing emi. a 4.7f capacitor is capable of this task, but only if it is placed close to the lt8606 (see the pcb layout section). a second precaution regarding the ceramic input capaci - tor concerns the maximum input voltage rating of the lt8606. a ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. if the lt8606 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the lt8606 s voltage rating. this situation is easily avoided (see analog devices application note 88). output capacitor and output ripple the output capacitor has two essential functions. along with the inductor, it filters the square wave generated by the lt8606 to produce the dc output. in this role it determines the output ripple, thus low impedance at the switching frequency is important. the second function is to store energy in order to satisfy transient loads and sta - bilize the lt8606s control loop. ceramic capacitors have very low equivalent series resistance (esr) and provide the best ripple performance. a good starting value is: c out = 100 v out ? f sw where f sw is in mhz, and c out is the recommended output capacitance in f. use x5r or x7r types. this choice will provide low output ripple and good tran - sient response. transient performance can be improved with a higher value output capacitor and the addition of a feedforward capacitor placed between v out and fb. increasing the output capacitance will also decrease the output voltage ripple. a lower value of output capacitor can be used to save space and cost but transient per - formance will suffer and may cause loop instability. see the typical applications in this data sheet for suggested capacitor values. when choosing a capacitor, special attention should be given to the data sheet to calculate the effective capaci - tance under the relevant operating conditions of voltage bias and temperature. a physically larger capacitor or one with a higher voltage rating may be required. ceramic capacitors ceramic capacitors are small, robust and have very low esr. however, ceramic capacitors can cause problems when used with the lt8606 due to their piezoelectric nature. when in burst mode operation, the lt8606 s switching frequency depends on the load current, and at very light loads the lt8606 can excite the ceramic capacitor at audio frequencies, generating audible noise. since the lt8606 operates at a lower current limit during burst mode operation, the noise is typically very quiet to a casual ear. if this is unacceptable, use a high performance tantalum or electrolytic capacitor at the output. a final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the lt8606. as pre - viously mentioned, a ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. if the lt8606 circuit is plugged into a live supply, the input voltage can ring to twice its nomi - nal value, possibly exceeding the lt8606s rating. this situation is easily avoided (see analog devices application note 88). enable pin the lt8606 is in shutdown when the en pin is low and active when the pin is high. the rising threshold of the en comparator is 1.05v, with 50mv of hysteresis. the en pin can be tied to v in if the shutdown feature is not used, or tied to a logic level if shutdown control is required. adding a resistor divider from v in to en programs the lt8606 to regulate the output only when v in is above a desired voltage (see block diagram). typically, this threshold, v in(en) , is used in situations where the input lt c8606 8606fb
16 for more information www.linear.com/lt8606 supply is current limited, or has a relatively high source resistance. a switching regulator draws constant power from the source, so source current increases as source voltage drops. this looks like a negative resistance load to the source and can cause the source to current limit or latch low under low source voltage conditions. the v in(en) threshold prevents the regulator from operating at source voltages where the problems might occur. this threshold can be adjusted by setting the values r3 and r4 such that they satisfy the following equation: v in(en) = r3 r4 + 1 ? ? ? ? ? ? ?1v where the lt8606 will remain off until v in is above v in(en) . due to the comparator s hysteresis, switching will not stop until the input falls slightly below v in(en) . when in burst mode operation for light-load currents, the current through the v in(en) resistor network can eas - ily be greater than the supply current consumed by the lt8606 . therefore, the v in(en) resistors should be large to minimize their effect on efficiency at low loads. intv cc regulator an internal low dropout (ldo) regulator produces the 3.5v supply from v in that powers the drivers and the internal bias circuitry. the intv cc can supply enough cur - rent for the lt8606 s circuitry and must be bypassed to ground with a minimum of 1f ceramic capacitor. good bypassing is necessary to supply the high transient currents required by the power mosfet gate drivers. applications with high input voltage and high switching frequency will increase die temperature because of the higher power dissipation across the ldo. do not connect an external load to the intv cc pin. output voltage tracking and soft-start (msop only) the lt8606 allows the user to program its output voltage ramp rate by means of the tr/ss pin. an internal 2a pulls up the tr/ss pin to intv cc . putting an external capacitor on tr/ss enables soft-starting the output to prevent current surge on the input supply. during the soft- start ramp the output voltage will proportionally track the applications information tr/ss pin voltage. for output tracking applications, tr/ ss can be externally driven by another voltage source. from 0v to 0.778v , the tr/ss voltage will override the internal 0.778v reference input to the error amplifier, thus regulating the fb pin voltage to that of tr/ss pin. when tr/ss is above 0.778v, tracking is disabled and the feed - back voltage will regulate to the internal reference voltage. an active pull-down circuit is connected to the tr/ss pin which will discharge the external soft-start capacitor in the case of fault conditions and restart the ramp when the faults are cleared. fault conditions that clear the soft-start capacitor are the en/uv pin transitioning low, v in voltage falling too low, or thermal shutdown. the lt8606 dfn does not have tr/ss pin or functionality. output power good when the lt8606s output voltage is within the 8.5% window of the regulation point, which is a v fb voltage in the range of 0.716v to 0.849v (typical), the output voltage is considered good and the open-drain pg pin goes high impedance and is typically pulled high with an external resistor. otherwise, the internal drain pull-down device will pull the pg pin low. to prevent glitching both the upper and lower thresholds include 0.5% of hysteresis. the pg pin is also actively pulled low during several fault conditions: en/uv pin is below 1v , intv cc has fallen too low, v in is too low, or thermal shutdown. synchronization (msop only) to select low ripple burst mode operation, tie the sync pin below 0.4v (this can be ground or a logic low out - put). to synchronize the lt8606 oscillator to an external frequency connect a square wave (with 20% to 80% duty cycle) to the sync pin. the square wave amplitude should have valleys that are below 0.9v and peaks above 2.7v (up to 5v). the lt8606 will not enter burst mode operation at low output loads while synchronized to an external clock, but instead will pulse skip to maintain regulation. the lt8606 may be synchronized over a 200khz to 2.2mhz range. the r t resistor should be chosen to set the lt8606 switching lt c8606 8606fb
17 for more information www.linear.com/lt8606 applications information frequency equal to or below the lowest synchronization input. for example, if the synchronization signal will be 500khz and higher, the r t should be selected for 500khz. the slope compensation is set by the r t value, while the minimum slope compensation required to avoid subhar - monic oscillations is established by the inductor size, input voltage, and output voltage. since the synchroniza - tion frequency will not change the slopes of the inductor current waveform, if the inductor is large enough to avoid subharmonic oscillations at the frequency set by r t , then the slope compensation will be sufficient for all synchro - nization frequencies. for some applications it is desirable for the lt8606 to operate in pulse-skipping mode, offering two major differ - ences from burst mode operation. first is the clock stays awake at all times and all switching cycles are aligned to the clock. second is that full switching frequency is reached at lower output load than in burst mode opera - tion as shown in figure?2 in an earlier section. these two differences come at the expense of increased quiescent current. t o enable pulse-skipping mode the sync pin is floated. for some applications, reduced emi operation may be desirable, which can be achieved through spread spec- trum modulation. this mode operates similar to pulse skipping mode operation, with the key difference that the switching frequency is modulated up and down by a 3khz triangle wave. the modulation has the frequency set by r t as the low frequency, and modulates up to approximately 20% higher than the frequency set by r t . to enable spread spectrum mode, tie sync to intv cc or drive to a voltage between 3.2v and 5v. the lt8606 does not operate in forced continuous mode regardless of sync signal. the lt8606 dfn is always programmed for burst mode operation and cannot enter pulse-skipping mode. shorted and reversed input protection the lt8606 will tolerate a shorted output. several features are used for protection during output short-circuit and brownout conditions. the first is the switching frequency will be folded back while the output is lower than the set point to maintain inductor current control. second, the bottom switch current is monitored such that if inductor current is beyond safe levels switching of the top switch will be delayed until such time as the inductor current falls to safe levels. this allows for tailoring the lt8606 to individual applications and limiting thermal dissipation during short circuit conditions. frequency foldback behavior depends on the state of the sync pin : if the sync pin is low, the switching frequency will slow while the output voltage is lower than the pro - grammed level. if the sync pin is connected to a clock sour ce, tied high or floated, the lt8606 will stay at the programmed frequency without foldback and only slow switching if the inductor current exceeds safe levels. there is another situation to consider in systems where the output will be held high when the input to the lt8606 is absent. this may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode ored with the lt8606 s output. if the v in pin is allowed to float and the en pin is held high (either by a logic signal or because it is tied to v in ), then the lt8606 s internal circuitry will pull its quiescent current through its sw pin. this is acceptable if the sys - tem can tolerate several a in this state. if the en pin is grounded the sw pin current will drop to near 0.7a. however, if the v in pin is grounded while the output is held high, regardless of en, parasitic body diodes inside the lt8606 can pull current from the output through the sw pin and the v in pin. figure 4 shows a connection of the v in and en/uv pins that will allow the lt8606 to run only when the input voltage is present and that protects against a shorted or reversed input. v in v in lt8606 gnd d1 8606 f04 en/uv figure 4. reverse v in protection lt c8606 8606fb
18 for more information www.linear.com/lt8606 applications information the ground plane as much as possible, and add thermal vias under and near the lt8606 to additional ground planes within the circuit board and on the bottom side. thermal considerations for higher ambient temperatures, care should be taken in the layout of the pcb to ensure good heat sinking of the lt8606. figure 5 shows the recommended component placement with trace, ground plane and via locations. the exposed pad on the bottom of the package must be soldered to a ground plane. this ground should be tied to large copper layers below with thermal vias; these lay - ers will spread heat dissipated by the lt8606 . placing additional vias can reduce thermal resistance further. the maximum load current should be derated as the ambient temperature approaches the maximum junction rating. power dissipation within the lt8606 can be estimated by calculating the total power loss from an efficiency measurement and subtracting the inductor loss. the die temperature is calculated by multiplying the lt8606 power dissipation by the thermal resistance from junction to ambient. the lt8606 will stop switching and indicate a fault condition if safe junction temperature is exceeded. pcb layout for proper operation and minimum emi, care must be taken during printed circuit board layout. note that large, switched currents flow in the lt8606 s v in pins, gnd pins, and the input capacitor (c in ). the loop formed by the input capacitor should be as small as possible by placing the capacitor adjacent to the v in and gnd pins. when using a physically large input capacitor the result - ing loop may become too large in which case using a small case/value capacitor placed close to the v in and gnd pins plus a larger capacitor further away is pre- ferred. these components, along with the inductor and output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. place a local, unbroken ground plane under the application circuit on the layer closest to the surface layer. the sw and boost nodes should be as small as possible. finally, keep the fb and rt nodes small so that the ground traces will shield them from the sw and boost nodes. the exposed pad on the bottom of the package must be soldered to ground so that the pad is connected to ground electrically and also acts as a heat sink thermally. to keep thermal resistance low, extend figure 5. pcb layout 8606 f05 gnd via v in via v out via en/uv via other signal via c out c in c bst c vcc ground plane on layer 2 r t l c in (opt) r1 c ff r2 r4 r3 r pg 1 c ss lt c8606 8606fb
19 for more information www.linear.com/lt8606 typical applications v in bst en/uv c1 0.1f c5 10pf r2 1m v in 5.5v to 42v c6 10nf c3 1f v out 5v 350ma power good r3 187k 8606 ta02 l1 10h sync intv cc tr/ss rt lt8606 gnd sw pg fb r4 100k r1 18.2k l1 = xfl3010-103me c4 10f x7r 0805 f sw = 2mhz c2 1f x7r 0805 v in bst en/uv c1 0.1f c5 10pf r2 1m v in 3.8v to 42v c6 10nf c3 1f v out 3.3v 350ma power good r3 309k 8606 ta03 l1 6.8h sync intv cc tr/ss rt lt8606 gnd sw pg fb r4 100k r1 18.2k l1 = xfl3010-682me c4 10f x7r 0805 f sw = 2mhz c2 1f x7r 0805 v in bst en/uv c1 0.1f c5 100pf r2 1m v in 12.7v to 42v c6 10nf c3 1f v out 12v 350ma power good r3 69.8k 8606 ta04 l1 47h sync intv cc tr/ss rt lt8606 gnd sw pg fb r4 100k r1 40.2k l1 = mss6132-473mlb c4 22f x7r 1210 f sw = 1mhz c2 4.7f x7r 1206 5v 2mhz step down 3.3v 2mhz step down 12v 1mhz step down lt c8606 8606fb
20 for more information www.linear.com/lt8606 v in bst en/uv c1 0.1f c5 10pf r2 1m v in 3.2v to 20v (42v transient) c6 10nf c3 1f v out 1.8v 350ma power good r3 768k 8606 ta05 l1 3.3h sync intv cc tr/ss rt lt8606 gnd sw pg fb r4 100k r1 18.2k l1 = xfl3010-332me c4 22f x7r 1206 f sw = 2mhz c2 4.7f v in bst en/uv c1 0.1f c5 47pf r2 1m v in 5.8 to 40v c6 10nf c3 1f v out 5v 350ma power good r3 187k 8606 ta06 l1 27h l3 4.7h l2 bead sync intv cc tr/ss rt lt8606 (msop) gnd sw pg fb r4 100k r1 60.4k c4 22f x7r 1206 f sw = 700khz c2 4.7f c9 33f c7 4.7f c8 4.7f c8, c7, c2: x7r 1206 c9: 63sxv33m l1: mss5121-273 l2: mpz2012s221at000 l3: xal4030-472 ultralow emi 5v 1.5a step down 1.8v 2mhz step down typical applications lt c8606 8606fb
21 for more information www.linear.com/lt8606 package description please refer to http://www.linear.com/product/lt8606#packaging for the most recent package drawings. msop (mse) 0213 rev i 0.53 0.152 (.021 .006) seating plane 0.18 (.007) 1.10 (.043) max 0.17 ?0.27 (.007 ? .011) typ 0.86 (.034) ref 0.50 (.0197) bsc 1 2 3 4 5 4.90 0.152 (.193 .006) 0.497 0.076 (.0196 .003) ref 8910 10 1 7 6 3.00 0.102 (.118 .004) (note 3) 3.00 0.102 (.118 .004) (note 4) note: 1. dimensions in millimeter/(inch) 2. drawing not to scale 3. dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.152mm (.006") per side 4. dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.152mm (.006") per side 5. lead coplanarity (bottom of leads after forming) shall be 0.102mm (.004") max 6. exposed pad dimension does include mold flash. mold flash on e-pad shall not exceed 0.254mm (.010") per side. 0.254 (.010) 0 ? 6 typ detail ?a? detail ?a? gauge plane 5.10 (.201) min 3.20 ? 3.45 (.126 ? .136) 0.889 0.127 (.035 .005) recommended solder pad layout 1.68 0.102 (.066 .004) 1.88 0.102 (.074 .004) 0.50 (.0197) bsc 0.305 0.038 (.0120 .0015) typ bottom view of exposed pad option 1.68 (.066) 1.88 (.074) 0.1016 0.0508 (.004 .002) detail ?b? detail ?b? corner tail is part of the leadframe feature. for reference only no measurement purpose 0.05 ref 0.29 ref mse package 10-lead plastic msop, exposed die pad (reference ltc dwg # 05-08-1664 rev i) lt c8606 8606fb
22 for more information www.linear.com/lt8606 package description please refer to http://www.linear.com/product/lt8606#packaging for the most recent package drawings. 2.00 0.05 (4 sides) 2.00 sq 0.05 note: 1. drawing is not a jedec package outline 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package 0.55 0.05 bottom view?exposed pad 0.23 ref 0.335 ref 0.335 ref 0.75 0.05 1 4 8 5 pin 1 bar top mark (see note 6) 0.200 ref 0.00 ? 0.05 (dc8ma) dfn 0113 rev ? 0.23 0.05 0.45 bsc 0.25 0.05 recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 0.90 ref 0.23 ref 0.85 0.05 1.8 ref 1.8 ref 2.60 0.05 package outline 0.45 bsc pin 1 notch r = 0.15 dc8 package 8-lead plastic dfn (2mm 2mm) (reference ltc dwg # 05-08-1939 rev ?) exposed pad variation aa lt c8606 8606fb
23 for more information www.linear.com/lt8606 information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent rights of analog devices. revision history rev date description page number a 06/17 added dfn package option clarified electrical parameters for dfn package option clarified graphs for msop package option clarified pin functions for dfn package option clarified operation section to include dfn option clarified applications last paragraph and figure 2 to include dfn option clarified applications section to include dfn operation added dfn package description 1,2 2,3 6,7 9 11 12 16,17 22 b 11/17 added h-grade option clarified oscillator frequency r t conditions clarified efficiency graphs clarified frequency foldback graph clarified switching waveform graph clarified block diagram added figure 5 clarified typical applications for msop package option 2, 3 3 4 7 8 10 18 20, 24 lt c8606 8606fb
24 ? analog devices, inc. 2017 lt 1117 ? printed in usa www.linear.com/lt8606 related parts typical application part number description comments lt8607 42v, 750ma, 92% efficiency, 2.2mhz synchronous micropower step-down dc/dc converter with i q? =?3a v in ?=?3v?to?42v, v out(min) ?=?0.778v, i q ?=?3a, i sd ?

▲Up To Search▲

Price & Availability of LTC8606

	To Download LTC8606 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .