BL8588 High Efficiency 1×/1.5× Charge Pump 4-Channels LED Driver DESCRIPTION FEATURES 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 1µF and two 0.47µF 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 VIN and reduces quiescent current to less than 1µA. APPLICATION • • • • • TYPICAL APPLICATION CIRCUIT BL8588 www.belling.com.cn 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 1 Programmable Current Sinks White LED Backlighting Cell Phones and Smart phones PDAs, Digital Cameras, and Camcorders Color (RGB) Lighting BL8588 PIN DISCRIPTIONS Pin No. Symbol 1 2 3 4 5 6 7 NC NC D4 D3 D2 D1 GND 8 VOUT 9 C2+ 10 C1+ 11 12 13 14 15 16 C1C2VIN PGND EN NC Description No connection No connection Channel 4 sink current input Channel 3 sink current input Channel 2 sink current input Channel 1 sink current input Signal ground Charge pump output to drive load circuit, a 1µF capacitor should be used to short this pin to ground. Flying capacitor 2 positive terminal. Connect a 1µF capacitor between C2+ and C2-. Flying capacitor 1 positive terminal. Connect a 1µF capacitor between C1+ and C1-. Flying capacitor 1 negative terminal. Flying capacitor 2 negative terminal. Power supply input, a 1µF capacitor is required to connect this pin to ground. Power ground Enable pin and can use this pin to program the sink current. No connection PIN CONFIGURATION NC EN PGND VIN 16 15 14 13 12 C2- NC 2 11 C1- LF YYNZZ NC 1 D4 3 10 D3 4 9 5 6 7 8 D2 D1 GND VOUT Marking ： LF: Product code YY: LOT NO. N: Fab code C1+ ZZ: Date code C2+ Top view QFN 3mm×3mm ORDERING INFORMATION Product NO Ordering Number Pin Package BL8588 BL8588CJKTR 3*3 QFN-16 Devices per reel 3K/reel Temperature range & Rohs -40~85°C & Pb free ABSOLUTE MAXIMUM RATING Item VIN Iomax TJ www.belling.com.cn Description Input supply voltage Maximum load current Operating junction temperature range 2 Value Unit -0.3-6 100 -40-150 mA V °C BL8588 ELECTRICAL CHARACTERISTICS CIN=COUT=1µF, C1=C2=0.47µF, Ta=25°C, unless otherwise noted. Symbol VIN V_UVLO IQ ISD ILED VTH Description Supply voltage range Under voltage-lockout threshold Quiescent operating current Shutdown current Sink current accuracy 1.5× mode to 1× mode transition threshold ROUT Open loop out resistance VEN Enable voltage TEN_PULSE VDROPOUT The positive and negative pulse width of EN pin D pin Dropout voltage ISHORT FOSC TSD Output short current Oscillator frequency Thermal shutdown temperature T_H Condition 1× mode/No load current 1.5× mode/No load current EN=0 ISET=20mA Min 2.8 2.5 Typical 0.3 Max 5.5 2.8 0.5 6 1 -10 +10 3.7 1x mode, (Vin-Vout)/Iout 1.5x mode, (1.5VinVout)/Iout Logic high voltage Logic low voltage Dimming control 1.2 0.4 Thermal shutdown hysteretic 20 120 0.7 100 1 150 30 µA % Ω 5 100% LED current setting (Note1) Short output to ground mA V 2.2 4 Unit V V V µS mV 1.3 mA MHZ °C °C Note1: Dropout voltage is defined as the D pin to GND voltage at which current into D pin drops 10% from the value at VD=0.2V. BLOCK DIAGRAM www.belling.com.cn 3 BL8588 TYPICAL CHARACTERISTICS LED Curent VS Dropout Voltage LED Current VS Pulse Number 25 20 LED Current(mA) LED Current(mA) 25 15 10 5 0 20 15 10 5 0 0 50 100 150 200 250 0 4 8 Dropout Voltage(mV) 14 26 13 LED Current(mA) LED Current(mA) 28 24 22 20 D1 18 D2 16 D3 14 D4 3.1 3.5 3.9 4.3 4.7 Input Voltage(V) 5.1 Quiescent Current(mA) 4 3 2 1 0 www.belling.com.cn 10 D1 D2 D3 D4 9 8 3.1 3.5 3.9 4.3 4.7 Input Voltage(V) 5 1.5X Mode 11 2.7 5.5 6 3.5 4.5 Input Voltage(V) 12 7 Quiescent Current VS Input Voltage 2.5 16 LED Current Matching VS Input Voltage (10mA/LED) LED Current Matching VS Input Voltage (20mA/LED) 2.7 12 Pulse Number 5.5 1X Mode 4 5.1 5.5 BL8588 OPERATION WAVEFORMS LED current LED current EN EN Fig. 2 Shutdown from EN pin Fig. 1 Startup from EN pin Output voltage ripple Input current Input voltage ripple LED current Output voltage ripple Input voltage ripple Fig. 4 Operating at 1x mode with 100% brightness Fig. 3 Operating at 1.5x mode with 100% brightness www.belling.com.cn 5 BL8588 DETAIL DESCRIPTION Startup sequence The BL8588 starts to work only when powered on and the EN pin became after a delay, the delay time is at least EN pin is not allowed to connect to directly or keep it floating. 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. VIN high 4us. VIN 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. Code _ No = Mod ( N ,16) , 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. 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 TD is about 20uS. The relationship between LEDs’ brightness and the Code_No is listed as the following table. Code No 0 1 2 3 4 5 6 7 ON duty EN Td=20uS Td=20uS 20mA I_LED Fig. 5 PWM 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 Code_No=1 Code_No=4 EN 20uS 20uS Iset/20mA=15/15 Iset/20mA=12/15 Fig. 6 Linear current Dimming Control www.belling.com.cn Code No 8 9 10 11 12 13 14 15 ISET/20mA 8/15 7/15 6/15 5/15 4/15 3/15 2/15 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. EN dimming control I_LE D ISET/20mA 0 1 14/15 13/15 12/15 11/15 10/15 9/15 6 BL8588 Short Circuit Protection lower supply voltage of 0.3V than a LED with VF of 3.5V. For the BL8588, the LED with dropout lower than 3.4V is adequate. 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. External Component 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. The driver requires two external 1µF 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 1µF is sufficient. In 1X mode, the device operates linearly and does not introduce switching noise to the supply. Thermal Protection Layout Consideration When the device temperature exceeds 150°C the driver enters a thermal protection shutdown mode. The IC resumes normal operation once the temperature drops by about 30°C to 120°C. Due to its high switching frequency and high transient current, careful consideration of PCB layout is necessary. The input capacitor (CIN) and the device, as well as the ground of CIN and COUT 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. LED selection LEDs with lower VF 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 VF of 3.2V can keep the device working in the 1X mode for www.belling.com.cn 7 BL8588 PACKAGE INFORMATION Package QFN3X3-16 www.belling.com.cn Devices per reel 8 3000 Unit mm