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| ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 1 BL9590 six-string white led driver with active current balancing for lcd panel applications features ? drives six parallel strings with multiple series- connected leds per string ? 1.5% current regulation accuracy between strings ? low 450mv feedback voltage at full current improves efficiency ? step-up controller regulates the output just above the highest led string voltage ? full-scale led current adjustable from 15ma to 25ma, or preset 20ma ? wide 100:1 dimming range ? programmable dimming control: direct dpwm or analog dimming ? built-in pll for synchronized dimming control ? open and short led protections ? output overvoltage protection ? wide input voltage range from 4.5v to 26v ? external mosfet allows a large number of leds per string ? 500khz/750khz/1mhz switching frequency ? small, 20-pin, 4mm x 4mm thin qfn package applications ? notebook, subnotebook, and tablet computer displays ? automotive systems ? handy terminals description the BL9590 is a high-efficiency driver for white light-emitting diodes (leds). it is designed for large liquid-crystal displays (lcds) that employ an array of leds as the light s ource. a current-mode step-up controller drives up to six parallel strings of multiple series-connected leds. each string is terminated with ballast that achieves 1.5% current regulation accuracy, ensuring even brightness for all leds. the BL9590 has a wide input-voltage range from 4.5v to 26v, and provides a fixed 20ma or adjustable 15ma to 25ma full-scale led current. the BL9590 has two dimming control modes to enable a wide variety of applications. in direct dpwm mode, the led current is directly turned on and off by a pwm signal. in analog dimming mode, an internal phase-locked loop (pll) circuit translates the pwm signal into an analog signal and linearly controls the led current down to 12.5%. below 12.5%, digital dimming is added to allow lower average led current down to 1%. both control methods provide 100:1 dimming range. the BL9590 has multiple features to protect the controller from fault conditions. separate feedback loops limit the output voltage if one or more leds fail open or short. the controller features cycle-by- cycle current limit to provide consistent operation and soft-start capability. a thermal shutdown circuit provides another level of protection. the step-up controller uses an external mosfet, which provides good efficiency and allows for scalable output power and maximum operating voltage. low feedback voltage at each led string (450mv) helps reduce power loss. the BL9590 features selectable switching frequency (500kh z, 750khz, or 1mhz), which allows trade-offs between external com- ponent size and operating efficiency. the BL9590 is available in a thermally en hanced, lead-free, 20-pin, 4mm x 4mm, thin qfn package. ordering information BL9590 ?x xxx typical application package: q20: qfn20 t20: tqfn20 features: p: standard (default, lead free) c: customized
ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietar y information. unauthor ized photocopy and du plication prohibited 3/2010 ?2010 belling all rights reserved 2 BL9590 six-string white led driver with active current balancing for lcd panel applications absolute maximum rating (note 1) in, /shdn, to gnd -0.3v to +28v fb_ to gnd -0.3v to +28v v cc , brt, ena, osc, ov to gnd -0.3v to +6v iset, ccv, cs to gnd -0.3v to v cc +0.3v fset, cpll, ext to gnd -0.3v to v cc +0.3v continuous power dissipation(t a =+70c) 20-pin thin qfn(derate 16.9m w/c above +70c) 1349mw maximum junction temperature 150c operating temperature range (note2) -40c to 85c storage temperature range -65c to 125c lead temperature (soldering, 10s) 300c package information thermal resistance (note 4) : package ? ja ? jc 4 x 4 mm tqfn 37 c/w 20c/w note 1: absolute maximum ratings are those values bey ond which the life of a device may be impaired. note 2: the BL9590 is guaranteed to meet perfo rmance specifications from 0c to 70 c. specifications over the ?40c to 85c operating temperature range are assured by design, characterization and correlation with statistical process controls. note 3: x x: product code y: year of manufacturing (9:2009) w: week of manufacturing (w:a-z, a-z) contact belling marketing for informa tion in detail. note 4: thermal resistance is specified with approximately 1 square of 1 oz copper. part number top mark temp range BL9590 x x y w (note3) -40c to +85c ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietar y information. unauthor ized photocopy and du plication prohibited 3/2010 ?2010 belling all rights reserved 3 BL9590 six-string white led driver with active current balancing for lcd panel applications pin description pin name function 1 osc oscillator frequency selection pin. connect osc to v cc to set the step - up converter?s oscillator frequency to 1mhz. connect osc to gnd to set the frequency to 500khz. float osc to set the frequency to 750khz. 2 ena analog dimming enable. ena sets the pwm control mode. set ena low to enable direct dpwm dimming. set ena high to enable analog dimming. in both modes, the duty cycle of the pwm signal at the brt input controls the led current characteristics. see the dimming control section for a complete description. 3 brt brightness control input. the duty cycle of this digital input signal controls the led current characteristics. the allo wable frequency range is 100hz to 500hz in analog dimming mode. the duty cycle can be 100% to 1%. the brt frequency can go above 500hz in direct dpwm mode as long as the brt pulse width is greater than 50 s minimum. see the dimming control section for a complete description. 4 /shdn shutdown control input. the BL9590 shuts down when /shdn is less than 0.8v. pulling /shdn above 2.1v enables the BL9590. /shdn can be connected to the input voltage if desired. 5 fb1 led string 1 cathode connection. fb1 is the open-drain output of an internal regulator, which controls current through fb1. fb1 can sink up to 27ma. if unused, connect fb1 to gnd. 6 fb2 led string 2 cathode connection. fb2 is the open-drain output of an internal regulator, which controls current through fb2. fb2 can sink up to 27ma. if unused, connect fb2 to gnd. 7 fb3 led string 3 cathode connection. fb3 is the open-drain output of an internal regulator, which controls current through fb3. fb3 can sink up to 27ma. if unused, connect fb3 to gnd. 8 gnd ground 9 fb4 led string 4 cathode connection. fb4 is the open-drain output of an internal regulator, which controls current through fb4. fb4 can sink up to 27ma. if unused, connect fb4 to gnd. 10 fb5 led string 5 cathode connection. fb5 is the open-drain output of an internal regulator, which controls current through fb5. fb5 can sink up to 27ma. if unused, connect fb5 to gnd. 11 fb6 led string 6 cathode connection. fb6 is the open-drain output of an internal regulator, which controls current through fb6. fb6 can sink up to 27ma. if unused, connect fb6 to gnd. 12 cs step-up controller current-sense inpu t. connect the cs input to a ground referenced sense resistor to measure the current in the external mosfet switch. 13 ext external mosfet gate-drive output 14 ov overvoltage sense. connect ov to the center tap of a resistive detection threshold for voltage limiting at ov is 1.23v (typ). 15 v cc 5v linear regulator output. v cc provides power to the BL9590 and is also used to bias the gate driver for the external mosfet. bypass v cc to gnd with a ceramic capacitor of 1 f or greater. if v in is less than or equal to 5.5v, connect v cc to in to the disable the internal ldo and use the external 5v supply to v cc . when /shdn is low, the internal linear regulator is disabled. ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietar y information. unauthor ized photocopy and du plication prohibited 3/2010 ?2010 belling all rights reserved 4 BL9590 six-string white led driver with active current balancing for lcd panel applications pin name function 16 in supply input. v in biases the internal 5v linear regulator that powers the device. bypass in to gnd directly at the pin with a 0.1 f or greater ceramic capacitor. 17 ccv step-up converter compensation pin. connect a 0.1 f ceramic capacitor and 1.2k ? resistor from ccv to gnd. wh en the BL9590 shuts down, ccv is discharged to 0v through an internal 20k ? resistor. 18 iset full-scale led current adjustment pin. the resistance from iset to gnd controls the full-scale current in each led string: i ledmax = 20ma x 100k ? /r iset the acceptable resistance range is 74k ? < r iset < 133k ? , which corresponds to full-scale led current of 27ma > i ledmax > 15ma. connect iset to vcc for a default full-scale led current of 20ma. 19 fset pll free-running frequency control pin. the resistance from fset to gnd controls the pll oscillato r?s free-running frequency, f pll : f pll = 1 / (10 x r fset x 800pf) the capture range is 0.6 x f pll to f pll . the acceptable resistance range for fset is 250k ? < r fset <754k ? , which corresponds to a frequency range of 500hz > f pll > 166hz. the resulting capture frequency range is 100hz to 500hz. 20 cpll phase-locked loop-compensation capacito r pin. the capacitance at cpll compensates the pll loop response. connect a 0.1 f ceramic capacitor from cpll to gnd. ep ep exposed backside pad. solder to the circ uit board ground plane with sufficient copper connection to ensure low thermal resistance. see the pcb layout guidelines section. ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietar y information. unauthor ized photocopy and du plication prohibited 3/2010 ?2010 belling all rights reserved 5 BL9590 six-string white led driver with active current balancing for lcd panel applications block diagram control and driver logic 5v linear regulator oscillator v cc tri-level comparator current sense slope compensation hvc lvc 8-bit dac osc 256xf brt + - + - sat + + - vcc+0.6v + + - - in v cc 1.25v ccv gm error amplifier iset ref adj fset - pll v cc -0.4v 8-bit counter 8-bit latch digital comparator digital control cpll brt ena ref clk /shdn osc error comparator output overvoltage comparator ov ext c s fb6 fb5 fb4 fb3 fb2 fb1 gnd fb2 fb3 fb4 fb5 fb6 8 5msbs 5lsbs 8 current source current source current source current source current source current source clock en fb overvoltage comparator 65ms timer shutdown latch ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietar y information. unauthor ized photocopy and du plication prohibited 3/2010 ?2010 belling all rights reserved 6 BL9590 six-string white led driver with active current balancing for lcd panel applications electrical characteristics (note 5) (v in =12v, v /shdn =v in, ccv=0.1 f, t a =0 to +85 , unless otherwise noted. typical values are at t a =+25 .) parameter conditions min typ max units v in =v cc 4.5 5.5 in input voltage range v cc =bypassed to gnd through 1uf capacitor 5.5 26.0 v v in =26v 1 2 in quiescent current v /shdn =high, brt=gnd v in =v cc =5v 1 2 ma v cc output voltage v /shdn =5v, 6v ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 8 BL9590 six-string white led driver with active current balancing for lcd panel applications operation the BL9590 is a high-efficiency driver for arrays of white leds. it contains a fixed- frequency, current m ode, pwm step-up controller, 5v linear regulator, dimming control circuit, and six regulated current sources (see figure 2). when enabled, the step-up controller boosts the output voltage to provide sufficient headroom for the current sources to regulate their respective string currents. the BL9590 features se- lectable switching frequency (500khz, 750khz, or 1mhz), which allows trade-offs between external component size and operating efficiency. the control architec- ture automatically skips pulses at light loads to improve efficiency and prevents overcharging the output capacitor. a pwm logic input signal, brt, controls the led brightness. the BL9590 supports both analog and digital control of the led current, and achieves 100:1 dimming range. the BL9590?s dimming control circuit consists of a pll, a digital comparator, and a dac. in direct dpwm mode, the step-up controller and current source are directly tu rned on and off by the pwm signal. in analog dimming mode, an internal pll, digita l comparator, and dac circuit translate the pwm signal into an analog signal that linearly controls the led current, down to a pwm duty factor of 12.5%. the BL9590 has multiple features to protect the controller fr om fault conditions. separate feedback loops limit the output voltage if one or more leds fail open or short. during operation, if one or more strings fails, the corresponding current sources are disabled after an internal timer expires. the remaining led strings still operate normally. if all strings fails, the controllers shuts down and latches off. the controller features cycle-by-cycle current limit to provide consistent operation and soft-start capability. a thermal-shutdown circuit provides another level of protection. the BL9590 includes a 5v linear regulator that provides the internal bias and gate drive for the step-up controller. when an external 5v is available, the internal ldo can be overdriven to decrease power dissipation. otherwise, connect the in pin to an input greater than 5.5v. the internal ldo is disabled when /shdn is low. u1 BL9590 /shdn vcc ena iset brt fset ccv cpll ep osc fb6 fb5 fb4 fb3 fb2 fb1 ext cs gnd ov in cin 0.1uf cout n1 rs 56m ? d1 1 2 l1 4.7uh 1 2 vout(up to 35v) vin(7v to 21v) 1uf r4 511k ? r3 1.2k ? r1 1m ? r2 37.4k ? 0.1uf 0.1uf figure 1. typical operating circuit ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 9 BL9590 six-string white led driver with active current balancing for lcd panel applications fixed frequency step-up controller the BL9590?s fixed-frequency, current- mode, step up controller automatically chooses the lowest active fb_ voltage to regulate the feedback vo ltage. specifically, the difference betwe en the lowest fb_ voltage and the current source-control signal plus an offset (v sat ) is integrated at the ccv output. the resulting error signal is compared to the exte rnal switch current plus slope compensation to terminate the switch on time. as the load changes, the error amplifier sources or sinks current to the ccv output to adjust the required peak inductor current. the slope-compensation signal is added to the current-sense signal to improve stability at high duty cycles. at light loads, the BL9590 automatically skips pulses to improve efficiency and prevent overcharging the output capacitor. in skip mode, the inductor current ramps up for a minimum on-time of approximately 150ns, then discharges the stored energy to the output. the switch remains off until another pulse is needed to boost the output voltage. internal 5v linear regulator vcc and uvlo the BL9590 includes an internal low- dropout linear regulator (v cc ). when v in is higher than 5.5v and /shdn is high, this linear regulator generates a 5v supply to power an internal pwm controller, control logic, and mosfet driver. this linear regulator can deliver at least 10ma of total additional load current. if v in is less than or equal to 5.5v, v cc and in can be connected together and powered from an external 5v supply. there is an internal diode from v cc to in, so v in must be greater than v cc (see figure 2). the BL9590 includes uvlo protection. the controller is disabled until v cc exceeds the uvlo threshold of 4.25v (typ). hysteresis on uvlo is approximately 20mv. the v cc pin should be bypassed to gnd with a 1 f or greater ceramic capacitor. external 5v supply u2 BL9590 /shdn vcc ena iset brt fset ccv cpll ep osc fb6 fb5 fb4 fb3 fb2 fb1 ext cs gnd ov in cin cout n1 rs 30m ? d1 1 2 l1 0.9uh 1 2 vout(up to 22v) vin(2.8v to 5.5v) 1uf r4 511k ? r3 1.2k ? r1 1m ? r2 59k ? 0.1uf 0.1uf figure 2 low-input-voltage application circuit ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 10 BL9590 six-string white led driver with active current balancing for lcd panel applications startup at startup, the BL9590 checks each fb_ pin to determine if the respective current string is enabled. each fb_ pin is internally pulled up with a 180 a current source. if an fb_ pin is connec ted to gnd, the corresponding string current source is disabled. this feedback scan takes app- roximately 4.2ms, after which the step-up converter begins switching. shutdown when the /shdn pin is less than 0.8v, the BL9590 shuts down the internal ldo, the reference, current sour ces, and all control circuitry. the result ing supply current is less than 10 a. while the n-channel mosfet is turned off, the step-up regulator?s output is connected to in through the external inductor and rectifier diode. frequency selection a tri-level osc input sets the internal oscillator frequency for the step-up converter, as shown in table 1. high- frequency (1mhz) operation optimizes the regulator for the smallest component size, at the expense of efficiency due to increased switching losses. low-frequency (500khz) operation offers the best overall efficiency, but requires larger components and pcb area. table 1 frequency selection osc switch frequency(khz) gnd 500 open 750 v cc 1000 overvoltage protection to protect the step- up converter when the load is open, or the output voltage becomes excessive for any reason, the BL9590 features a dedicated overvoltage feedback input (ov). the ov pin is connected to the center tap of a resistive voltage-divider from the high voltage output (see figure 1). when the BL9590 is power- ed up, if none of the led strings on fb1? fb6 are connected to the step-up converter output, the step-up converter regulates the output voltage to v out =1.23v(1 + r1 / r2). when v ov exceeds 1.23v, a comparator turns off n1. the step-up converter switch is reenabled after the output voltage drops below the protection threshold. led current sources maintaining uniform led brightness and dimming capability are critical for lcd backlight applications. the BL9590 is equipped with a bank of six matched current sources. these specialized current sources are accurate to within 1.5% and can be switched on and off within 10 s, enabling pwm frequencies of up to 2khz. all led full-scale currents are identical and are set through the iset pin (15ma < iled < 27ma). the minimum voltage drop across each current source is approximately 450mv at 20ma. the low voltage drop helps reduce dissipation while maintaining sufficient compliance to control the led current within the required tolerances. the led current sources can be disabled by grounding the respective fb_ pin at startup. when the ic is powered up, the controller scans settings for all fb_ pins. if an fb_ pin is not grounded, an internal ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 11 BL9590 six-string white led driver with active current balancing for lcd panel applications circuit pulls this pin high, and the controller enables the corresponding current source to regulate the string current. if the fb_ pin is grounded, the cont roller disables the corresponding current regulator. the current regulator c annot be disabled by grounding any of the fb_ pins after the ic is powered up. all fb_ pins in use are measured and the highest signal (hvc) and the lowest signal (lvc) are extracted for two feedback loops. hvc is used to identify excessive dis- sipation across the current-source inputs. when hvc is greater than v cc + 0.6v (typ) for greater than 65m s (see the current- source fault protection section), a fault latch is set and the BL9590 is shut down. the ldo output is not affected by the fault latch. lvc is fed into the step-up converter?s error amplifier to regulate the step-up converter?s output voltage. current-source fault protection the led current sour ces are protected against string open, short, and gross mismatch faults, using overvoltage detec- tion circuitry on each fb_ pin. if any of these three fault conditions persists for a preset duration, t he fault strings are disabled. the duration of the fault time depends on the dimming mode and the duty cycle of the brt input (d brt ). in the dpwm mode, the timeout interval is: t timeout_dpwm = 65ms/d brt in analog dimming mode, the fault time is fixed at 65ms for d brt greater than 12.5%. when d brt is less than 12.5%, the timeout interval is: t timeout_analog = 8.125ms/d brt the fault latch can be cleared by cycling the power or togglin g the shutdown pin /shdn. open-current source protection the BL9590 step-up converter output voltage is regulated according to the minimum value of the enable fb_ voltages. if an individual led string is open, the respective fb_ is pulled down to near ground. in this situation, the step-up converter output voltage increases but is clamped to a level set with the ov feedback input. when this elevated output voltage is applied to the undamaged strings, excessive voltage drop develops across the fb_ pins. if the resulting hvc signal exceeds v cc + 0.6v for greater than 65ms, the fault string s are disabled to protect the circuit. led-short and string mismatch protection normally, white leds have variations in forward-voltage drop of 3.1v to 3.6v. the BL9590 can tolerate slight mismatches between led strings. when the sum of the led forward voltages creates a mismatch in the strings so the hvc signal exceeds v cc + 0.6v for greater than 65ms, the fault condition circuit is triggered in much the same way as the circ uit responds to open string faults. similar protection is activated when an led is short ed. the larger the number of series-connected leds (n), the smaller the tolerable mismatch between leds: 0.6 sat cc n error v v v <+ ? 450 sat vmv and 5 cc vv = 5.150 n error v < average error per led 5.150 v n = for n = 8, the aver age error per led = 644mv. ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 12 BL9590 six-string white led driver with active current balancing for lcd panel applications for n = 10, the average error per led = 510mv. the larger the total mismatch, the larger the voltage drop required across each current source to corr ect for the error, and therefore the larger the dissipation within the BL9590. dimming control the BL9590 features both analog and digital dimming control. analog dimming can provide potentially higher converter efficiency because of low voltage drop across each wled when the current is low. digital dimming (dpwm) provides less wled color distortion since the wled current is held at full scale when the wled is on. the BL9590?s dimming control circuit consists of a pll, a digital comparator, and a dac. the contro ller provides 100:1 dimming range through either analog or digital control methods. both methods translate the duty cycle of the brt input into a control signal for the led current sources. in analog dimming mode, the current-source outputs are dc and the brt duty cycle (12.5% < d brt < 100%) modulates the amplit ude of the currents. for d brt < 12.5%, the led current is digitally modulated to reduce the average led current down to 1% of full scale. the pll detects the brt frequency and phase, and adjusts the current-source amplitude and duty cycle synchronously (see figure 4). in digital dimming mode, the step-up controller and current source are directly turned on and off by the pwm signal. the current pulse magnitude, or full-scale current, is set by iset and is independent of pwm duty factor. the current-source outputs are pwm signals synchronized to the brt input signal (see figure 5). the full-scale current in both methods is specified by resistance from the iset pin to ground: max 20 100 iset led ma k i r = the acceptable resistance range is 74k ? < r iset <133k ? , which corresponds to full- scale led current of 27ma > i ledmax > 15ma. connect iset to vcc for a default full-scale led current of 20ma. when ena is high, the analog dimming is enabled, when ena is low, digital dimming is enabled. when the current-source output is pulse- width modulated, current-source turn-on is synchronized with the brt signal. synchronization and low jitter in the pwm signals help reduce flicker noise in the display. the current through each fb_ pin is controlled only during the step-up converter?s on-time. during the converter?s off-time, the current so urces are turned off. the output voltage does not discharge and stays high. each fb_ pin can withstand 28v, which is the pin?s maximum rated voltage. table 2 summarizes the characteristics of both analog and digital dimming methods. a pll translates the duty cycle of the brt input into a reference for the BL9590?s current sources. a resi stor from the fset pin to ground controls the pll?s free running frequency: 1 10 800 pll fset f r pf = the pll?s loop filter bandwidth is set with a capacitor from the cpll pin to ground. this filter integrates the phase difference between the brt input signal and the pll oscillator. the filter bandwidth determines the pll?s dynamic response to frequency changes in the brt signal. for most applications, a 0.1 f capacitor is adequate ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 13 BL9590 six-string white led driver with active current balancing for lcd panel applications for oscillator frequencies in the 166hz < f pll < 500hz range. the pll frequency capture window is 0.6 x f pll to f pll . the pll is disabled in dpwm mode; consequently, the brt frequency is not limited by f pll . the maximum brt frequency is determined by the minimum brt on-time of 50 s and the minimum acceptable dimming factor. if a 1% dimming factor is needed, the maximum brt frequency is 200hz. if a 10% dimming factor is acceptable, the maximum brt frequency is 2khz. on b rt t d t = figure 3.led current contro l using analog dimming mode on b rt t d t = figure 4. led current cont rol using dpwm dimming mode table 2.dimming mode mode ena pll frequency cpll description analog+dpwm >2.1v 250 k ? ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 14 BL9590 six-string white led driver with active current balancing for lcd panel applications in analog dimming mode, load-current tran- sients can occur when the brt frequency abruptly changes on the fly. large regulation transients induce a flash on the led load that is observable with the naked eye and should therefor e be avoided. such annoying flashes can be eliminated by dynamically changing the ena pin setting. when a capacitor is connected to the cpll pin and the ena pin is grounded, the pll continues to run but does not affect the dimming. when fast pll lockup transitions are require d, the ena pin can be momentarily pulled to ground; after the pll is locked up, ena can be pulled high to reenable pll in dimming control. table 3. component list circuit figure1 figure 1 figure 1 figure 2 switching frequency 1mhz 750khz 500khz 750khz white led 3.2v(typ), 3.5v (max) at 20ma nichia nssw008c 3.2v(typ), 3.5v (max) at 20ma nichia nssw008c 3.2v(typ), 3.5v (max) at 20ma nichia nssw008c 3.2v(typ), 3.5v (max) at 20ma nichia nssw008c number of white leds 6 series x 6 parallel, 20ma (max) 8series x 6 parallel, 20ma (max) 10series x 6parallel, 25ma (max) 6series x 6parallel, 20ma (max) input voltage 4.5v to 5.5v, vcc = in 7v to 21v 7v to 21v 2.8v to 5.5v, vcc = 5v inductor l1 2.2 h , 2.5a power inductor sumida cdrh5d16-2r2 4.7 h , 2.05a power inductor sumida cdrh5d16-4r7 4.7 h , 3.6a power inductor sumida cdrh8d28-4r7 0.9 h, 4.7a power inductor sumida cdrh5d16-0r9 input capacitor 10 f 10%, 10v x5r ceramic capacitor (1206) murata grm31mr61a106k 10 f 10%, 25v x5r ceramic capacitor (1206) murata grm 31c r61e 106ka 10 f 10%, 25v x5r ceramic capacitor (1206) murata grm 31c r61e 106ka 10 f 10%, 10v x5r ceramic capacitor (1206) murata grm 31m r61a 106k c out output capacitors 2.2 f 10%, 50v x7r ceramic capacitor (1x) murata grm31cr71h225k 2.2 f 10%, 50v x7r ceramic capacitor (1206)(1x) murata grm31cr71h225k 4.7 f 10%, 50v x7r ceramic capacitor (1210) (1x) murata grm32er71h475k 2.2 f 10%, 50v x7r ceramic capacitor (1x) murata grm31cr71h225k mosfet n1 30v, 3a n-channel mosfet (6-pin sc70) vishay si1402dh 60v, 2.8a n-channel mosfet(6-pin tsop) fairchild semiconductor fdc5612 sanyo semiconductor cph6424 60v , 6a n- channel mosfet ( power pak 1212- 8) vishay si7308dn 30v, 4.9a n-channel mosfet (6-pin tsop) vishay si3456bdv diode rectifier d1 2a, 30v schottky diode nihon ec21qs03l 2a, 40v schottky diode toshiba cms11 nihon ec21qs04 3a, 60v schottky diode nihon ec31qs06 3a, 30v schottky diode nihon ec31qs03l sense resistor 50m ? 1%, 1/2w irc lrc-lrf- 1206lf-01-r050-f 56m ? 1%, 1/2w irc lrc-lrf- 1206lf-01-r056-f 40m ? 1%, 1/2w irc lrc-lrf- 1206lf-01-r040-f 30m ? 1%, 1/2w irc lrc-lrf- 1206lf-01-r030-f ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 15 BL9590 six-string white led driver with active current balancing for lcd panel applications table 4. component suppliers supplier phone website murata 770-436-1300 www.murata.com nichia 248-352-6575 www.nichia.com sumida 847-545-6700 www.sumida.com toshiba 949-455-2000 www.toshiba.com/taec vishay 203-268-6261 www.vishay.com thermal shutdown the BL9590 includes a thermal-protection circuit. when the local ic temperature exceeds +170 (typ), the controller and current sources shut down and do not restart until the die temperature drops by 15 . application information all BL9590 designs should be prototyped and tested prior to production. table 3 provides a list of pow er components for the typical applications circuit. table 4 lists component suppliers. external component value choice is primarily dictated by the output voltage and the maximum load current, as well as maximum and minimum input voltages. begin by selecting an inductor value. once l is known, choose the diode and capacitors. inductor selection the inductance, peak current rating, series resistance, and physical size should all be considered when sele cting an inductor. these factors affect the converter?s operating mode, efficiency, maximum output load capability, transient response time, output voltage ripple, and cost. the maximum output current, input voltage, output voltage, and switching frequency determine the inductor value. very high inductance minimizes the current ripple, and therefore reduces the peak current, which decreases core losses in the inductor and i 2 r losses in the entire power path. however, large inductor values also require more energy storage and more turns of wire, which increases physical size and i 2 r copper losses in the inductor. low inductor values decrease the physical size, but increase the current ripple and peak current. finding the best inductor involves the compromises among circuit efficiency, inductor size, and cost. when choosing an inductor, the first step is to determine the operating mode: continuous conduction mode (ccm) or discont inuous conduction mode (dcm). the bl 9590 has a fixed internal slope compensation, which re- quires a minimum inductor value. when ccm mode is chosen, the ripple current and the peak current of the inductor can be minimized. if a small-size inductor is required, dcm mode can be chosen. in dcm mode, the inductor value and size can be minimized but the inductor ripple current and peak current are higher than those in ccm. the controller can be stable, independent of the internal slope com- pensation mode, but t here is a maximum inductor value requirement to ensure the dcm operating mode. the equations used here include a constant lir, which is the ratio of the inducto r peak-to-peak ripple ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 16 BL9590 six-string white led driver with active current balancing for lcd panel applications current to the average dc inductor current at the full-load current. the controller operates in dcm mode when lir is higher than 2.0, and it switches to ccm mode when lir is lower than 2.0. the best trade- off between inductor size and converter efficiency for step-up regulators generally has an lir between 0.3 and 0.5. however, depending on the ac characteristics of the inductor core material and ratio of inductor resistance to other power-path resistances, the best lir can shift up or down. if the inductor resistance is relatively high, more ripple can be accepted to reduce the number of required tu rns and increase the wire diameter. if the inductor resistance is relatively low, increasing inductance to lower the peak current can reduce losses throughout the power path. if extremely thin high-resistance inductors are used, as is common for lcd panel applications, lir higher than 2.0 can be chosen for dcm operating mode. once a physical inductor is chosen, higher and lower values of the inductor should be evaluated for efficiency improvements in typi cal operating regions. the detail design procedure can be described as follows: calculate the approximate inductor value using the typical input voltage (v in ), the maximum output current (i out(max) ), the expected efficiency ( typ ) taken from an appropriate curve in the typical operating chara- cteristics, and an estimate of lir based on the above discussion: 2 __ () typ in min out in min out out max osc vvv l vi flir ?? ? ?? ?? = ?? ?? ?? ?? ?? ?? the BL9590 has a minimum inductor value limitation for stable operation in ccm mode at low input voltage because of the internal fixed slope compensation. the minimum inductor value for stability is calculated by the following equation: () ( () () (2) 51 out max diode in min s ccm min osc min vvvr l mv f + ? = where 51mv is a scale factor based on slope compensation, and r s is the current- sense resistor. to determine the minimum inductor value, the r s can be temporarily calculated using the following equation: () 100 1.2 stmp in dcmax mv r i ? = where 100mv is the current-limit sense voltage. the minimum inductor value should be recalculated after the rs is determined (see the sense-resistor selection section). choose an available inductor value from an appropriate inductor family. calculate the maximum dc input current at the minimum input voltage v in(min) , using conservation of energy and the expected efficiency at that operating point ( min ) taken from an appropriate curve in the typical operating characteristics: () () () out max out in dcmax in min min iv i v = calculate the ripple current at that operating point and the peak current required for the inductor: () ( ) () () () in min out max in min ripple out max osc vv v i lv f ? = (, ) 2 ripple peak in dc max i ii =+ when dcm operating mode is chosen to minimize the inductor value, the cal- culations are different from that in the above ccm mode. the maximum inductor value for dcm mode is calculated by the following equation: () () () 2 () () () () 1 2 in min dcm max out max diode in min osc max out max out max v l vv v fv i ?? = ? ?? + ?? ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 17 BL9590 six-string white led driver with active current balancing for lcd panel applications the peak inductor current in dcm mode is calculated using the follo wing equation: () () () () () ( ) 2( ) () out max out max out max diode in min peak osc min out max diode ivvvv i lf v v + ? = + the inductor?s saturation current rating should exceed i peak and the inductor?s dc current rating should exceed i in(dc,max) . for good efficiency, choose an inductor with less than 0.1 ? series resistance. considering the typica l operating circuit, the maximum load current (i out(max) ) is 120ma with a 28.72v output and a minimal input voltage of 7v. choosing a dcm operating mode and estimating efficiency of 90% at this operating point: () 2 7 1 28.72 0.4 (7 ) 0.9 5.8 2 0.825 28.72 120 dcm max v l vv v h m hz v ma ?? =? ?? + ?? = an inductance less than l dcm(max) is required, so a 4.7 h inductor is chosen. the peak inductor current at minimum input voltage is calculated as follows: 120 2 28.72 (28.72 0.4 7 ) 1.35 4.7 0.675 0.9 (28.72 0.4 ) peak ma v v v i a hmhz vv + ? == + sense-resistor selection the detected signal is fed into the step-up converter control compensation loop through the cs pin. the BL9590?s current- mode step-up converter senses the switch current from cs to gnd with an external resistor, r s . the current-limit sense vol- tage is a fixed 100mv. the required resistance is calculated based upon the peak inductor current at the end of the switch on-time: _ 25.6 (0.75 ) cs ec max s peak vmvd r i +? < where 25.6mv is a scale factor from slope compensation, v cs_ec is the current-sense voltage listed in the electrical characte ristics table (85mv), and the d max is the maximum duty cycle at minimum input voltage and maximum output voltage. in dcm operating mode, it is calculated by the following equation: () lim osc max in min li f d v = for the typical operating circuit as figure 1: 4.7 1.35 0.75 0.68 7 max hamhz d v == 85 25.6 (0.75 0.68) 64 1.35 s mv mv r m a + ? < = again, r s is calculated as a maximum, so a 56m ? current-sense resistor is chosen. the total output volt age ripple has two components: the capacit ive ripple caused by the charging and discharging on the output capacitor, and the ohmic ripple due to the capacitor?s equivalent series re- sistance (esr): () ( ) ripple ripple c ripple esr vv v = + () () () () () out max out max in min ripple c out out max osc iv v v cvf ?? ? ?? ?? and: () ( ) ripple esr peak esr cout vir = where i peak is the peak inductor current (see the inductor selection section). the output voltage-ripple voltage should be low enough for the fb_ current-source regulation. the ripple voltage should be less than 200mv p-p . for ceramic capa- citors, the output-volt age ripple is typically dominated by v ripple (c). the voltage rating and temperature characteristics of the output capacitor must also be considered. external mosfet selection the BL9590?s step-up converter uses an external mosfet to enable applications ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 18 BL9590 six-string white led driver with active current balancing for lcd panel applications with scalable output voltage and output power. the boost switching architecture is simple and ensures t hat the controller is never exposed to high voltage. only the external mosfet, diode, and inductor are exposed to the output voltage plus one schottky diode forward voltage: __ _ bv f led f schottky fb vnv v v = + + the mosfet?s breakdown ratings should be higher than v bv with sufficient margin to ensure long-term reliability. a conservative rule of thumb, a minimum 30% margin would be recommended for mosfet breakdown volt age. the external mosfet should have a current rating of no less than the i peak derived from the inductor selection section. to improve efficiency, choose a mosfet with low r ds(on) . the BL9590?s gate-drive linear regulator can provide 10ma. select the external mosfet with a total gate charge so the average curr ent to drive the mosfet at maximum switching frequency is less than 10ma: () 10 gmax osc qfma < for example, the si3458dv is specified with 16nc of max total gate charge at vg = 10v. for 5v of gate drive, the required gate charge is 8nc, wh ich equates to 8ma at 1mhz the mosfet conduction loss or resistive loss is caused by the mosfet?s on-resistance (r ds(on) ). this power loss can be estimated as: 3 () () () 3 d s on osc peak res max in min rlfi pd v = for the above si3458dv, the estimated conduction loss is: 3 () 0.1 4.7 750 1.35 0.04 37 res max hkhz a p dw v ? == the approximate maximu m switching loss can be calculated as: () 2 turn off peak out osc sw max tivf pd ? = for the above si3458dv, the approximate switching loss is: () 10 1.35 28.72 750 0.145 2 sw max ns a v khz p dw == rectifier diode selection the BL9590?s high switching frequency demands a high-speed rectifier. schottky diodes are recommended for most app- lications because of thei r fast recovery time and low forward volta ge. the diode should be rated to handle the output voltage and the peak switch current. make sure that the diode?s peak current rating is at least i peak calculated in the inductor selection section and that its breakdown voltage exceeds the output voltage. setting the overvoltag e protection limit the ov protection circuit should ensure the circuit safe operation; therefore, the controller should limit the output voltage within the ratings of all mosfet, diode, and output capacitor components, while providing sufficient output voltage for led current regulation. the ov pin is connected to the center tap of a resistive voltage divider (r1 and r2 in figure 1) from the high-volt age output. when the controller detects the ov pin voltage reaching the threshold v ov_th , typically 1.23v, ov protection is activated. hence, the step-up converter output overvoltage protection point is: () _ 1 (1 ) 2 out ovp ov th r vv r =+ in figure 1, the output ovp voltage is set to: () 1 1.23 (1 ) 34.1 37.4 out ovp m vv v k =+ = ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 19 BL9590 six-string white led driver with active current balancing for lcd panel applications input capacitor selection the input capacitor (c in ) filters the current peaks drawn from the input supply and reduces noise injection into the ic. a 10 f ceramic capacitor is used in the typical operating circuit (figure 1) because of the high source impedance seen in typical lab setups. actual applications usually have much lower source impedance since the step-up regulator often runs directly from the output of another regulated supply. in some applications, c in can be reduced below the values used in the typical operating circuit. ensure a low noise supply at in by using adequate c in . alternatively, greater voltage variation can be tolerated on c in if in is decoupled from c in using an rc lowpass filter. select c in ?s rms ripple current rating to ensure that its thermal rise is less than approximately 10c: 23 l rms di i = led selection and bias the series/parallel conf iguration of the led load and the full-scale bias current have a significant effect on regulator performance. led characteristics vary significantly from manufacturer to manufacturer. consult the respective led data sheets to determine the range of output vo ltages for a given brightness and led current. in general, brightness increases as a function of bias current. this suggests that the number of leds could be decreased if higher bias current is chosen; however, high current increases led temperature and reduces operating life. impr ovements in led technology are resulting in devices with lower forward voltage while increasing the bias current and light output. led manufacturers specify led color at a given led current. with lower led current, the color of the emitted light tends to shift toward the blue range of the spectrum. a blue bias is often acceptable for business applications but not for high- image-quality applications such as dvd players. direct dpwm dimming is a viable solution for reducing power dissipation while maintaining led color integrity. careful attention should be paid to switching noise to avoid other display quality problems. using fewer leds in a string improves step-up converter efficiency, and lowers breakdown voltage requirements of the external mosfet and diode. the minimum number of leds in series should always be greater than the maximum input voltage. if the diode voltage drop is lower than the maximum input voltage, the vo ltage drop across the current-sense inputs (fb_) increases and causes excess heating in the ic. between 8 and 12 leds in series is ideal for input voltages up to 20v. led vfb_ variation the BL9590 has accurate (1.5%) match- ing for each current source. however, the forward voltage of each white led can vary up to 5% from part to part. the accumulated voltage difference in each string equates to additional power loss within the ic. for the best efficiency, the voltage difference between strings should be minimized. the difference between lowest voltage string and highest voltage string should be less than 4.5v. otherwise, the internal led short-circuit protection shuts the part off. choosing the appropriate dimming mode ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 20 BL9590 six-string white led driver with active current balancing for lcd panel applications analog dimming mode allows lower peak led current and results in higher converter efficiency and lower noise compared to direct dpwm mode. unfortunately, the led color spectrum can shift as a function of dc current so dpwm mode is often used to achieve more consistent display characteristics. (see the led manufac- turer?s data sheet to determine the extent of the color shift.) when the BL9590 is configured with an fset resistor and cpll capacitor, the ena signal can toggle between modes on the fly. care should be exercised when switching between modes to prevent the current from becoming unstable during the pll lock-in time. to avoid such problems, force the controller into dpwm mode between transitions. lcd panel capacitance some lcd panels include a capacitor in parallel with led string to improve esd immunity. the BL9590 can start up without a problem for string capacitance up to 0.27 f. pcb layout guidelines careful pcb layout is important for proper operation. use the following guidelines for good pcb layout: 1) minimize the area of the high current- switching loop of the rectifier diode, external mosfet, sense resistor, and output capacitor to avoid excessive switching noise. use wide and short traces for the gate-drive loop from the ext pin, to the mosfet gate, and through the current-sense resistor, then returning to the ic gnd pin. 2) connect high-curr ent input and output components with short and wide connections. the high-current input loop goes from the positive terminal of the input capacitor to the induct or, to the external mosfet, then to the current-sense resistor, and to the input capacitor?s negative terminal. the high-current output loop is from the positive terminal of the input capacitor to the inductor, to the rectifier diode, to the positive terminal of the output capacitors, reconnecting between the output capacitor and input capacitor ground terminals. avoid using vias in the high-curr ent paths. if vias are unavoidable, use multiple vias in parallel to reduce resistance and inductance. 3) create a ground is land (pgnd) con- sisting of the input and output capacitor ground and negative terminal of the current-sense resistor. connect all these together with short, wi de traces or a small ground plane. maximizing the width of the power ground traces improves efficiency and reduces output-voltage ripple and noise spikes. create an analog ground island (agnd) consisting of the over- voltage detection-divider ground con- nection, the iset and fset resistor connections, ccv and cpll capacitor connections, and the device?s exposed backside pad. connect the agnd and pgnd islands by connecting the gnd pins directly to the expos ed backside pad. make no other connections between these separate ground planes. 4) place the overvoltage detection-divider resistors as close to t he ov pin as possible. the divider?s center trace should be kept short. placing the resistors far away causes the sensing trace to become antennas that can pick up switching noise. avoid running the sensing traces near lx. 5) place the in pin bypass capacitor as close to the device as possible. the ground connection of the in bypass capacitor should be connected directly to ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 21 BL9590 six-string white led driver with active current balancing for lcd panel applications gnd pins with a wide trace. 6) minimize the size of the lx node while keeping it wide and short. keep the lx node away from the feedback node and ground. if possible, avoid running the lx node from one side of t he pcb to the other. use dc traces as shields, if necessary. 7) refer to the BL9590 evaluation kit for an example of proper board layout. in 16 vc c 15 cc v 17 shdn 4 en a 2 iset 18 fset 19 cp ll 20 br t 3 ex t 13 cs 12 dv 14 gn d 8 osc 1 fb1 5 fb2 6 fb3 7 fb4 9 fb5 10 fb6 11 u1 bl 9 59 0 c7 10 f/ 2 5v vi n 7v to 26v pgnd1 vcc 4.5v to 5.5v ju1 c8 op en c5 2.2 f/ 5 v c6 op en r7 short c1 0.1 f 1 2 3 vcc c2 1 f c1 7 op en r8 1.2k c3 0.1 f vo ut shdn fb6 gn d br t fb5 fb4 fb3 fb1 fb2 vl ed r9 100k ju2 vi n ju3 vcc c9 op en c1 0 op en c4 0.1 f r1 51k ju4 ju5 r3 value 511k vcc r1 0 100k l1 4.7uh lx ex t cs r6 56m ? r5 1m 1% r4 37.4k 1% vo ut ju13 vcc ju6 r1 1 op en vi n r1 2 op en r1 3 op en r1 4 op en r1 5 op en r1 6 op en c1 1 op en jf1 jf2 jf3 jf4 jf5 jf6 c1 2 op en c1 3 op en c1 4 op en c1 5 op en c1 6 op en ju7 ju8 ju9 ju10 ju11 ju12 gn d1 pgnd vi n vout vl ed d 1 d 2 g 3 s 4 d 5 d 6 n1 fdc5612 cs 1 2 3 r1 8 1 2 3 r2 1 2 3 r1 7 d1 ze ne r1 d2 le d d3 le d d4 le d d5 le d d6 le d d7 le d d8 le d d9 le d d1 0 le d d1 1 le d d12 led d13 led d14 led d15 led d16 led d17 led d18 led d19 led d20 led d21 led d2 2 le d d2 3 le d d2 4 le d d2 5 le d d2 6 le d d2 7 le d d2 8 le d d2 9 le d d3 0 le d d3 1 le d d3 2 le d d3 3 le d d3 4 le d d3 5 le d d3 6 le d d3 7 le d d3 8 le d d3 9 le d d4 0 le d d4 1 le d d42 led d43 led d44 led d45 led d46 led d47 led d48 led d49 led d50 led d51 led d5 2 le d d5 3 le d d5 4 le d d5 5 le d d5 6 le d d5 7 le d d5 8 le d d5 9 le d d6 0 le d d6 1 le d figure 5: BL9590 layout circuit. ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 22 BL9590 six-string white led driver with active current balancing for lcd panel applications 1 1 2 3 2 1 4 4 1 2 3 3 2 1 4 4 1 2 3 3 2 1 4 3 2 1 4 1 1 2 1 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 1 2 2 1 1 2 2 1 2 1 1 2 1 2 1 2 1 2 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 3 1 2 2 1 2 3 1 2 1 1 2 1 2 3 1 2 3 3 2 1 1 2 3 1 2 3 1 2 3 3 2 1 5 1 2 3 4 6 1 2 1 3 1 2 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 3 1 2 3 1 2 1 1 1 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 2 1 2 1 1 2 2 1 2 1 1 2 2 1 1 2 1 2 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 1 1 1 1 1 1 1 2 1 2 1 1 3 0 2 1 3 2 1 4 4 1 2 3 3 2 1 4 4 1 2 3 3 2 1 4 3 2 1 4 1 1 1 3 1 2 2 1 2 3 1 2 1 1 2 1 2 3 1 2 3 3 2 1 1 2 3 1 2 3 1 2 3 3 2 1 1 3 1 2 3 1 2 3 1 2 1 1 1 1 1 1 1 1 1 1 1 2 1 figure 6: top layer layout figure 7:bottom layer layout ppmic bu www.belling.com.cn BL9590 rev 0.3 belling proprietary in formation. unauthorized photoc opy and duplication prohibited 3/2010 ?2010 belling all rights reserved 23 BL9590 six-string white led driver with active current balancing for lcd panel applications package description |
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