RT9373A 3-Channel Charge Pump White LED Driver with Low Dropout Current Source General Description Features The RT9373A is a high efficiency and cost effective charge pump white LED driver. It supports up to 3 white LEDs with regulated constant current for uniform intensity. The RT9373A maintains the highest efficiency by utilizing a x1/x1.5/x2 charge pump and low dropout current regulators. z Very High Efficiency Over 80% of Battery Life z Support up to 3 White LEDs Support Up to 60mA Output Current 1% Typical LED Current Matching Soft Start Function Auto Charge Pump Mode Selection 250kHz Fixed Frequency Oscillator Output Over Voltage Protection 16 Steps Brightness Control Low Input Noise and EMI RoHS Compliant and 100% Lead (Pb)-Free z z z z z z z z RT9373A is available in a WQFN3x3-16L package. Applications Ordering Information z Pin Configurations Richtek products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area. DS9373A-04 April 2011 16 15 14 13 NC NC GND C1P 1 12 2 11 3 10 17 4 9 5 6 7 8 VOUT ` VIN Note : LED2 LED1 (TOP VIEW) C1N Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) z LED3 Package Type QW : WQFN-16L 3x3 (W-Type) z VIN RT9373A Mobile Phone, DSC, MP3 White LED Backlighting LCD Display Supply C2N User can easily configure each LED current from 1.25mA to 20mA by a pulse dimming control. The dimming of white LEDs current can be achieved by applying a pulse signal to the EN pin. There are totally 16 steps of current could be set by users. z EN NC GND C2P WQFN-16L 3x3 www.richtek.com 1 RT9373A Typical Application Circuit C PUMP2 1uF V CC 2.8V to 5.5V 5, 13 C IN 2.2uF 12 GPIO 9 6 C2N 7 C1N C1P 4 C2P C PUMP1 1uF VOUT VIN RT9373A EN LED3 LED2 LED1 3, 10 GND 8 C OUT 2.2uF 16 15 14 Figure 1. For 3-WLEDs Application Circuit V CC 2.8V to 5.5V GPIO 5, 13 C IN 2.2uF 12 9 6 C2N 7 C1N C1P 4 C PUMP2 1uF C2P C PUMP1 1uF VIN EN VOUT RT9373A LED3 8 C OUT 2.2uF 16 LED2 15 3, 10 GND LED1 14 Figure 2. For 2-WLEDs Application Circuit www.richtek.com 2 DS9373A-04 April 2011 RT9373A Functional Pin Description Pin No. Pin Name 1, 2, 11, NC 17 (Exposed Pad) Pin Function No Internal Connection. 3 GND Ground. 4 C1P Positive Terminal of Bucket Capacitor 1 5 VIN Power Input Voltage. 6 C2N Negative Terminal of Bucket Capacitor 2. 7 C1N Negative Terminal of Bucket Capacitor 1. 8 VOUT Output Voltage Source. 9 C2P Positive Terminal of Bucket Capacitor 2. 10 GND Ground. 12 EN Chip Enable (Active High). Note that this pin is high impedance. 13 VIN Power Input Voltage. 14 LED 1 Output Current for LED1. (If not in use, pin should be connected to GND). 15 LED 2 Output Current for LED2. (If not in use, pin should be connected to GND). 16 LED 3 Output Current for LED3. (If not in use, pin should be connected to GND). C2N x1/x1.5/x2 Charge Pump VIN UVLO Shut Down Delay (2ms) EN C2P C1N C1P Function Block Diagram VOUT Current Limitation Soft Start Circuit 16 Steps Pulse Dimming Controller Low Drop Out Current Source (PMOS) LED3 LED2 LED1 GND DS9373A-04 April 2011 www.richtek.com 3 RT9373A Absolute Maximum Ratings z z z z z z z z (Note 1) Supply Input Voltage -----------------------------------------------------------------------------------------------------Other I/O Pin Voltage ----------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WQFN-16L 3x3 -----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WQFN-16L 3x3, θJA ------------------------------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Mode) ---------------------------------------------------------------------------------------------MM (Machine Mode) ------------------------------------------------------------------------------------------------------ Recommended Operating Conditions z z −0.3V to 6V −0.3V to 6V 1.47W 68°C/W 150°C 260°C −40°C to 150°C 2kV 200V (Note 4) Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 2.5V to 5.5V, CIN = COUT = CFLY = 1uF (ESR = 30mΩ), TA = 25°C, unless otherwise specification) Parameter Symbol Test Condition Min Typ Max Units 2.8 -- 5.0 V 1.6 2.1 2.5 V -- 100 -- mV 0.5 1 2 mA 1.5 2.5 5 mA 0 0.1 10 uA VTS_x1.5 VF = 3.5V, IOUT = 80mA, ILEDx = 20mA -- 3.75 -- V VF = 3.5V, IOUT = 80mA, ILEDx = 20mA -- 3.0 -- V -- 150 -- mV 1.25 -- 20 mA ILED-ERR 100% Setting −8 -- +8 % 100% Setting −5 -- +5 % 1.5 -- -- V -- -- 0.4 V Input Input Supply Voltage VIN Under-Voltage Lockout Threshold Under-Voltage Lockout Hysteresis VIN Rising Quiescent of x1 Mode IQ_x1 Quiescent of x2 Mode IQ_x2 Shutdown Current x1 mode to x1.5 mode Transition Voltage (V IN Falling) x1.5 mode to x2 mode Transition Voltage (V IN Falling) Hysteresis of Mode Transition x1 Mode, No Load, All LED pins connected to GND, VIN = 4V x2 Mode, No Load, All LED pins floating, VIN = 3.5V Enable = 0.4V, V IN = 2.8V to 5.5V VTS_x2 Output Current Range of ILEDx ILEDx Accuracy 2.8 < V IN < 5.5@V F = 3.2, IOUT = 60mA Current Matching Enable Logic-High Voltage V IH EN Threshold Logic-Low Voltage V IL To be continued www.richtek.com 4 DS9373A-04 April 2011 RT9373A Parameter Symbol Test Condition Min Typ Max Units EN Low Time for Dimming TIL 0.5 -- 500 us EN High Time for Dimming TIH 0.5 -- -- us EN Current High Current IIH V IH = V IN -- 1 10 uA Low Current IIL V IL = GND -- 1 10 uA TSHDN Pulse Dimming -- 2 -- ms -- 250 -- kHz EN Low Time for Shut Down Frequency Oscillator Frequency fOSC Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability. Note 2. θJA is measured in the natural convection at T A = 25°C on a low effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard. Note 3. Devices are ESD sensitive. Handling precaution is highly recommended. Note 4. The device is not guaranteed to function outside its operating conditions. DS9373A-04 April 2011 www.richtek.com 5 RT9373A Typical Operating Characteristics Efficiency vs. Input Voltage LED Current vs. Input Voltage 21.0 95 VF = 3.2V VF = 3.3V 90 LED2 LED3 85 20.0 Efficiency (%) LED Current (mA) 20.5 LED1 19.5 19.0 80 75 70 65 60 18.5 55 18.0 50 2.5 3 3.5 4 4.5 5 2.6 5.5 3 3.4 Input Voltage (V) 4.2 4.6 5 5.4 5.8 Input Voltage (V) Shutdown Current vs. Input Voltage Quiescent Current vs. Input Voltage 1.5 4.5 Quiescent Current (mA) 4 Shutdown Current (uA) 3.8 1.2 0.9 0.6 0.3 x2 Mode 3.5 3 2.5 2 x1 Mode 1.5 1 0.5 0 0 2.5 3 3.5 4 4.5 5 5.5 2.6 3.1 Input Voltage (V) 4.1 4.6 5.1 5.6 Input Voltage (V) Oscillator Frequency vs. Input Voltage Enable Voltage vs. Input Voltage 300 1.20 EN Voltage Threshold (V) Oscillator Frequency (kHz) 3.6 250 200 150 100 50 1.15 1.10 1.05 Rising 1.00 0.95 Falling 0.90 0.85 0 0.80 2.5 3 3.5 4 4.5 Input Voltage (V) www.richtek.com 6 5 5.5 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) DS9373A-04 April 2011 RT9373A Dimming Operation VIN (2V/Div) VOUT (2V/Div) VIN = 3.3V Dimming Operation VIN (2V/Div) VOUT (2V/Div) EN (2V/Div) EN (2V/Div) I LED (20mA/Div) ILED (20mA/Div) Time (1ms/Div) Time (1ms/Div) x1 Mode Inrush Current Response x1.5 Mode Inrush Current Response VIN (2V/Div) VIN (2V/Div) VOUT (5V/Div) VOUT (5V/Div) EN (2V/Div) EN (2V/Div) IIN (500mA/Div) VIN = 3.6V VIN = 4.2V, CIN = COUT = 2.2uF, CPUMP = 1uF IIN (500mA/Div) VIN = 3.7V, CIN = COUT = 2.2uF, CPUMP = 1uF Time (25us/Div) Time (100us/Div) x2 Mode Inrush Current Response x2 Mode EN Pin Shutdown Response VIN = 3V, CIN = COUT = 2.2uF, CPUMP = 1uF CIN = COUT = 2.2uF, CPUMP = 1uF C2N (2V/Div) VIN (2V/Div) VOUT (5V/Div) EN (2V/Div) VOUT (5V/Div) EN (2V/Div) ILED (500mA/Div) IIN (500mA/Div) Time (100us/Div) DS9373A-04 April 2011 Time (500us/Div) www.richtek.com 7 RT9373A x1.5 Mode Ripple & Spike x2 Mode Ripple & Spike VIN = 3.3V, CIN = COUT = 2.2μF VIN = 3.0V, CIN = COUT = 2.2μF VIN ac (100mV/Div) VIN ac (100mV/Div) VOUT ac (200mV/Div) VOUT ac (200mV/Div) C2N (2V/Div) C2N (2V/Div) Time (1us/Div) www.richtek.com 8 Time (1us/Div) DS9373A-04 April 2011 RT9373A Applications Information 20mA that is sufficient for most application in backlight. The dimming of white LEDs' current can be achieved by applying a pulse signal to the EN pin. There are totally 16 steps of current could be set by users. The detail operation of brightness dimming is showed in the Figure 3. The RT9373A is a high efficiency charge pump white LED driver. It provides 3 channels low dropout voltage current source to regulated 3 white LEDs current. For high efficiency, the RT9373A implements a smart mode transition for charge pump operation. The RT9373A provides pulse dimming function for LED brightness control. Selecting Capacitors To get the better performance of RT9373A, the selecting of peripherally appropriate capacitor and value is very important. These capacitors determine some parameters such as input and output ripple, power efficiency, maximum supply current by charge pump, and start-up time. To reduce the input and output ripple effectively, the low ESR ceramic capacitors are recommended. Generally, to reduce the output ripple, increasing the output capacitance COUT is necessary. However, this will increase the startup time of output voltage. For LED driver applications, the input voltage ripple is more important than output ripple. Input ripple is controlled by input capacitor CIN, increasing the value of input capacitance can further reduce the ripple. Practically, the input voltage ripple depends on the power supply’ s impedance. If a single input capacitor CIN cannot satisfy the requirement of application, it is necessary to add a low-pass filter. C-R-C filter used to reduce input ripple. The flying capacitor CPUMP1 and CPUMP2 determine the supply current capability of the charge pump. The lower value will limit the LED’ s current at low input voltage. Soft Start The RT9373A includes a soft start circuit to limit the inrush current at power on and mode switching. Soft start circuit limits the input current before output voltage reaching a desired voltage level. When the soft start off, the RT9373A won't sink spike current from VIN. Mode Decision The RT9373A uses a smart mode decision method to select the working mode for maximum efficiency. The charg pump can operation at x1, x1.5 or x2 mode. The mode decision circuit senses the output and LED voltage for up/down selection. Brightness Control The RT9373A implements the pulse dimming method being used to control the brightness of white LEDs. The part implements a 4-bit DAC for brightness control. Users can easily configure the LED current from 1.25mA to 20mA by a serial pulse. The maximum LED current is up to 30us < tREADY 0.5us < t HI EN Shutdown ILEDX 0 1 2 3 2ms < tSHDN 0.5us < tLO < 500us 4 5 100% 15/16 14/16 13/16 12/16 14 15 0 1 100% 2/16 1/16 15/16 Shutdown Figure 3. Brightness control by pulse dimming. RT9373A implements 16 steps brightness control DS9373A-04 April 2011 www.richtek.com 9 RT9373A Layout Consideration The RT9373A is a low dropout current source for white LED driver. Careful PCB layout is necessary. For best performance, place all peripheral components as close to the IC as possible. A short connection is highly recommended. The following guidelines should be strictly followed when designing a PCB layout for the RT9373A. 1. All the traces of LED pins running from chip to LEDs should be wide and short to reduce the parasitic connection resistance. 2. Input capacitor (CIN) should be placed close to VIN (Pin 5) and connected to ground plane. The trace of VIN in the PCB should be placed far away the sensitive devices or shielded by the ground. 3. The GND should be connected to a strong ground plane for heat sinking and noise protection. 4. Output capacitor (COUT) should be placed close to VOUT and connected to ground plane to reduce noise coupling from charge pump to LEDs. 5. The traces running from pins to flying capacitor should be short and wide to reduce parasitic resistance and prevent noise radiation. LED3 LED2 LED1 VIN 16 15 14 13 All the traces of LED pins running from chip to LEDs should be wide and short to reduce the parasitic connection resistance. GND 3 10 GND C1P 4 9 C2P C1 8 NC VOUT 11 7 2 C1N NC 6 EN C2N 12 5 1 VIN NC The traces running from pins to flying capacitor should be short and wide to reduce parasitic resistance and prevent noise radiation. C IN Ground Plane C2 C OUT Battery The GND should be connected to a strong ground plane for heat sinking and noise protection. Output capacitor (C OUT ) should be placed close to V OUT and connected to ground plane to reduce noise coupling from charge pump to LEDs. Input capacitor (C IN ) should be placed close to V IN (Pin 5) and connected to ground plane. The trace of V IN in the PCB should be placed far away the sensitive devices or shielded by the ground. Figure 4. PCB Layout Guide www.richtek.com 10 DS9373A-04 April 2011 RT9373A Outline Dimension D SEE DETAIL A D2 L 1 E E2 e b A A1 1 1 2 2 DETAIL A Pin #1 ID and Tie Bar Mark Options A3 Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 D 2.950 3.050 0.116 0.120 D2 1.300 1.750 0.051 0.069 E 2.950 3.050 0.116 0.120 E2 1.300 1.750 0.051 0.069 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 16L QFN 3x3 Package Richtek Technology Corporation Richtek Technology Corporation Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 5F, No. 95, Minchiuan Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)86672399 Fax: (8862)86672377 Email: [email protected] Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek. DS9373A-04 April 2011 www.richtek.com 11