www.belling.com.cn 1 high efficiency 1 /1.5 charge pump 4-channels led driver b l8588 description BL8588 is a low noise, high efficiency, and constant frequency charge pump dc/dc converter for white led application. the operation frequency is 1mhz. BL8588 works in load switch (1 ) and fractional (1.5 ) modes with four independent control outputs, each channel can provide 20ma constant current precisely from a 2.8v to 5.5v supply. only two external 1 m f and two 0.47 m f capacitors are required to build a compact and low-cost power supply solution. BL8588 uses en pin for simple on/off control and single wire serial pulse dimming in 16 steps. a low current shutdown feature disconnects the load from v in and reduces quiescent current to less than 1a. features input range: 2.8-5.5v 1% led current accuracy 20ma driver capacity each channel auto 1 /1.5 mode switchover pwm dimming control serial-pulse dimming control in linear 16 steps short-circuit protection thermal shutdown 1mhz constant switching frequency 3mm 3mm qfn package application programmable current sinks white led backlighting cell phones and smart phones pdas, digital cameras, and camcorders color (rgb) lighting typical application circuit BL8588
www.belling.com.cn 2 BL8588 pin discriptions pin no. symbol description 1 nc no connection 2 nc no connection 3 d4 channel 4 sink current input 4 d3 channel 3 sink current input 5 d2 channel 2 sink current input 6 d1 channel 1 sink current input 7 gnd signal ground 8 vout charge pump output to drive load circuit, a 1f cap acitor should be used to short this pin to ground. 9 c2+ flying capacitor 2 positive terminal. connect a 1f capacitor between c2+ and c2-. 10 c1+ flying capacitor 1 positive terminal. connect a 1f capacitor between c1+ and c1-. 11 c1- flying capacitor 1 negative terminal. 12 c2- flying capacitor 2 negative terminal. 13 vin power supply input, a 1 m f capacitor is required to connect this pin to grou nd. 14 pgnd power ground 15 en enable pin and can use this pin to program th e sink current. 16 nc no connection pin configuration vin vinvin vin gnd gnd gnd gnd en enen en nc ncnc nc nc ncnc nc d dd d1 11 1 d dd d2 22 2 d dd d3 33 3 d dd d4 44 4 c cc c1 11 1- -- - c cc c1 11 1+ ++ + c cc c2 22 2- -- - c cc c2 22 2+ ++ + vout vout vout vout pgnd pgnd pgnd pgnd nc ncnc nc 16 1616 16 15 1515 15 l l l l f f f f y y y y y y y y n n n n z z z z z z z z 1 11 1 2 22 2 3 33 3 4 44 4 5 55 5 6 66 6 7 77 7 9 99 9 10 1010 10 11 1111 11 12 1212 12 13 1313 13 14 1414 14 8 88 8 top view qfn 3mm 3mm ordering information product no ordering number pin package devices per reel temperature range & rohs BL8588 BL8588cjktr 3*3 qfn-16 3k/reel -40~85 c & pb free absolute maximum rating item description value unit vin input supply voltage -0.3-6 v iomax maximum load current 100 ma tj operating junction temperature range -40-150 c marking lf: product code yy: lot no. n: fab code zz: date code
www.belling.com.cn 3 BL8588 electrical characteristics c in =c out =1 m f, c 1 =c 2 =0.47 m f, t a =25 c, unless otherwise noted. symbol description condition min typical max unit v in supply voltage range 2.8 5.5 v v_ uvlo under voltage-lockout threshold 2.5 2.8 v i q quiescent operating current 1 mode/no load current 0.3 0.5 ma 1.5 mode/no load current 6 i sd shutdown current en=0 1 m a i led sink current accuracy i set =20ma -10 +10 % v th 1.5 mode to 1 mode transition threshold 3.7 v r out open loop out resistance 1x mode, (vin-vout)/iout 2.2 w 1.5x mode, (1.5vin- vout)/iout 5 v en enable voltage logic high voltage 1.2 v logic low voltage 0.4 t en _ pulse the positive and negative pulse width of en pin dimming control 4 20 m s v dropout d pin dropout voltage 100% led current setting (note1) 120 mv i short output short current short output to ground 100 ma f osc oscillator frequency 0.7 1 1.3 mhz tsd thermal shutdown temperature 150 c t_ h thermal shutdown hysteretic 30 c note1: dropout voltage is defined as the d pin to g nd voltage at which current into d pin drops 10% fr om the value at v d =0.2v . block diagram
www.belling.com.cn 4 BL8588 typical characteristics led curent vs dropout voltage 0 5 10 15 20 25 0 50 100 150 200 250 dropout voltage(mv) led current(ma) led current vs pulse number 0 5 10 15 20 25 0 4 8 12 16 pulse number led current(ma) led current matching vs input voltage (20ma/led) 14 16 18 20 22 24 26 28 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 input voltage(v) led current(ma) d1 d2 d3 d4 led current matching vs input voltage (10ma/led) 7 8 9 10 11 12 13 14 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 input voltage(v) led current(ma) d1 d2 d3 d4 quiescent current vs input voltage 0 1 2 3 4 5 6 2.5 3.5 4.5 5.5 input voltage(v) quiescent current(ma) 1.5x mode 1x mode
www.belling.com.cn 5 BL8588 operation waveforms fig. 1 startup from en pin fig. 2 shutdown from en pin fig. 3 operating at 1.5x mode with 100% brightness fig. 4 operating at 1x mode with 100% brightness en led current led current en input voltage ripple output voltage ripple led current input voltage ripple output voltage ripple input current
www.belling.com.cn 6 BL8588 detail description startup sequence the BL8588 starts to work only when vin powered on and the en pin became high after a delay, the delay time is at least 4us. en pin is not allowed to connect to vin directly or keep it floating. the BL8588 starts with 1x mode, the output follows closely to the supply voltage. if the average voltage of pin d1 to d4 falls below 0.25v the ic switches to 1.5x mode, and it can automatically switch back to 1x mode when the input voltage is higher than 3.7v. pwm dimming control if the frequency of the pwm signal to the en pin is less than 5khz, the average led current is proportional to the duty cycle of the pwm signal, and the en works as a simple on/off control. a high level turns on and a low shuts down the leds. there is a delay time between the input pwm signal and the output led current waveform, as shown in fig.5, the t d is about 20us. i_led 20ma td=20us on duty td=20us en fig. 5 pwm dimming control en dimming control the leds brightness can also be controlled by the pulses applied to the en pin, refer to the fig. 6. inside the device there is a 4-bit counter connecting to the en pin. the led current can be programmed up to 16 levels depends on the number of rise edges of the input waveform. a high level input (1) with pulse width wider than 20us is regarded as a signal to stop the build-in counter. the time between two wide high levels (more than 20us) is a counting period. when some rise edges occur between two high level pulses of 20us, the equation as shown below can calculate the active pulse number, called code_no. ) 16, ( _ n mod no code = , in the equation, n is the number of rise edges of the input waveform and mod function returns the remainder of n divided by 16. for example, if n=0, 16, or other integral multiple of 16, the mod function returns a value of 0, if n=1, 17 or other integral multiple of 16 plus 1, the mod function returns a value of 1, and so on. the relationship between leds brightness and the code_no is listed as the following table. code no i set /20ma code no i set /20ma 0 0 8 8/15 1 1 9 7/15 2 14/15 10 6/15 3 13/15 11 5/15 4 12/15 12 4/15 5 11/15 13 3/15 6 10/15 14 2/15 7 9/15 15 1/15 the frequency of the input pulse should be lower than 100khz, and the width of the high level and low level larger than 4us to prevent false trigger. code_no=1 code_no=4 iset/20ma=15/15 20us 20us en i_le d iset/20ma=12/15 fig. 6 linear current dimming control
www.belling.com.cn 7 BL8588 short circuit protection if the voltage difference between vout pin and any of a d pin exceeds 1v, for example, a led is shorted in the circuit, the corresponding channel will be shutdown internally by the ic. connect all unused leds to vout to avoid the accuracy reduction of the threshold of switching to 1.5x, and it also avoids wasting battery current. if the vout is shorted to ground, the BL8588 will stop operating and keep a constant source current of about 100ma until the short circuit is removed. thermal protection when the device temperature exceeds 150c the driver enters a thermal protection shutdown mode. the ic resumes normal operation once the temperature drops by about 30c to 120c. led selection leds with lower v f are recommended. from the efficiency perspective. it keeps the driver in the 1x mode longer hence helps improve the efficiency and extends battery life. for example, a white led with a v f of 3.2v can keep the device working in the 1x mode for lower supply voltage of 0.3v than a led with v f of 3.5v. for the BL8588, the led with dropout lower than 3.4v is adequate. external component the driver requires two external 1f ceramic capacitors for decoupling input, output, and for the charge pump. both capacitors type of x5r and x7r are recommended for the led driver application. in charge pump modes, the input current ripple is kept minimal. an input bypass capacitor of 1f is sufficient. in 1x mode, the device operates linearly and does not introduce switching noise to the supply. layout consideration due to its high switching frequency and high transient current, careful consideration of pcb layout is necessary. the input capacitor (c in ) and the device, as well as the ground of c in and c out should be placed as close as possible. to achieve best performance, it is recommended to minimize the distance between components. maximum trace width is recommended for connection. make sure each device connects to immediate ground plane. the use of multiple via improves the package heat dissipation.
www.belling.com.cn 8 BL8588 package information package qfn3x3-16 devices per reel 3000 unit mm
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