® RT9378 4 CHs 100mA x1/x1.5/x2 Charge Pump White LED Driver General Description Features The RT9378 is a 4 CH WLED driver with auto mode selection of x1, x1.5 and x2 mode with low dropout voltage in current sources. The RT9378 can power up to 4 white LEDs with regulated constant current for uniform intensity. Each channel (LED1 to LED4) can support up to 25mA. The part maintains highest efficiency by utilizing x1/x1.5/ x2 fractional charge pump and low dropout current regulators. For the brightness control, user can easily use a PWM signal generated from GPIO to control the brightness of WLEDs. z Efficiency Up to 93% Over Li-ion Battery Discharge z Typical 85% Average Efficiency Over Li-ion Battery Discharge Support Up to 4 White LEDs Support Up to 25mA/Per Channel Support Up to 100mA Output Current PWM Brightness Control 60mV Typical Current Source Dropout 1% Typical LED Current Accuracy 0.7% Typical LED Current Matching Automatic x1/x1.5/x2 Charge Pump Mode Transition Low Input Noise and EMI Charge Pump 5V Over Voltage Protection Power On/Mode Transition In-rush Protection 1MHz Switching Frequency 0.4μ μA Low Shutdown Current RoHS Compliant and Halogen Free The RT9378 is available in a WQFN-12L 2x2 package. Small 0.22μF capacitors can be used for fly capacitors. It provides the best backlighting solution with high efficiency and smallest board space for portable application. z z z z z z z z z z z Ordering Information z RT9378 z z Package Type QW : WQFN-12L 2x2 Lead Plating System G : Green (Halogen Free and Pb Free) Applications z z Note : Pin Configurations Richtek products are : ` Camera Phone, Smart Phone White LED Backlighting RoHS compliant and compatible with the current (TOP VIEW) C2N VOUT LED4 requirements of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. 12 11 10 C1N GND C1P Typical Application Circuit 1 9 GND 2 13 3 4 VIN 2.8V to 4.5V 3 C1P CFLY2 0.22µF 5 VIN 6 EN PWM Dimming 2, Exposed pad (13) GND RT9378 LED1 LED2 LED3 LED4 VOUT Marking Information 7 8 9 10 11 COUT 1µF Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS9378-04 January 2014 6 WQFN-12L 2x2 12 4 1 C1N C2P C2N CIN 1µF 7 LED3 LED2 LED1 C2P VIN EN CFLY1 0.22µF 5 8 For marking information, contact our sales representative directly or through a Richtek distributor located in your area. is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT9378 Functional Pin Description Pin No. Pin Name 1 C1N 2 GND 13 (Exposed Pad) 3 C1P Pin Function Fly Capacitor 1 Negative Connection. Ground Pin. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Fly Capacitor 1 Positive Connection. 4 C2P Fly Capacitor 2 Positive Connection. 5 VIN Power Input. 6 EN Chip Enable (Active High). 7 LED1 Current Sink for LED1. (If not in use, connect this pin to VIN) 8 LED2 Current Sink for LED2. (If not in use, connect this pin to VIN) 9 LED3 Current Sink for LED3. (If not in use, connect this pin to VIN) 10 11 LED4 VOUT Current Sink for LED4. (If not in use, connect this pin to VIN) Charge Pump Output. 12 C2N Fly Capacitor 2 Negative Connection. Function Block Diagram C1N C2P C2N C1P VIN VOUT Soft Start Circuit + Gate Driver 1MHz OSC Mode Decision Vr1 - Min VDS UVLO LED1 LED2 LED3 LED4 PWM Dimming Controller Shutdown Delay EN 2µA GND Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 Current Source Current Bias OVP is a registered trademark of Richtek Technology Corporation. DS9378-04 January 2014 RT9378 Absolute Maximum Ratings z z z z z z z z (Note 1) Supply Input Voltage, VIN -----------------------------------------------------------------------------------------------Output Voltage, VOUT ----------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WQFN-12L 2x2 -----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WQFN-12L 2x2, 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 5V −5V to 0.3V 0.606W 165°C/W 150°C 260°C −65°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 = 3.6V, VF = 3.5V, CIN = COUT = 1μF, CFLY1 = CFLY2 = 0.22μF, ILED1 to LED4 = 15mA, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit 2.8 -- 4.5 V 1.8 2 2.5 V -- 100 -- mV Input Power Supply Input Supply Voltage Under-Voltage Lockout Threshold Under-Voltage Lockout Hysteresis VIN VUVLO VIN Rising ΔVUVLO Quiescent Current IQ x1 Mode -- 1 2 mA Shutdown Current ISHDN VIN = 4.5V -- 0.4 2 μA ILEDx Accuracy ILEDx = 25mA −5 0 5 % Current Matching ILEDx = 25mA −2 0 2 % -- 1 -- MHz Minimum Turn On > 20μs 1 -- 4 kHz x1 Mode to x2 Mode Transition Voltage (VIN Falling) IOUT = 100mA, ILEDx = 25mA -- 3.6 3.8 V Mode Transition Hystersis IOUT = 100mA, ILEDx = 25mA -- 200 -- mV VIN – VOUT -- 5 -- V LED Current Charge Pump Oscillator Frequency PWM Dimming Frequency fOSC Mode Decision Protection Function OVP Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS9378-04 January 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT9378 Parameter Symbol Test Conditions Min Typ Max Unit 3 -- -- ms Enable EN Low Time for Shutdown EN Threshold Voltage Logic-Low VIL -- -- 0.2 V Logic-High VIH 1 -- -- V -- 2 -- μA EN Pull Low Current 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 TA = 25°C on a low effective single layer thermal conductivity test board of JEDEC 51-3 thermal measurement standard. The case point of θJC is on the exposed pad for the WQFN package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS9378-04 January 2014 RT9378 Typical Operating Characteristics LED Current vs. Input Voltage Efficiency vs. Input Voltage 100 30 90 28.5 27 LED Current (mA) 80 Efficiency (%) 70 60 50 40 30 25.5 LED1 LED2 LED3 LED4 24 22.5 21 19.5 18 20 10 16.5 LED VF = 3.42V 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 LED VF = 3.42V 15 0 2.8 5 3 3.2 3.4 3.6 3.8 5 x2 Mode Quiescent Current vs. Input Voltage x1 Mode Quiescent Current vs. Input Voltage 1 4 0.95 3.75 3.5 Quiescent Current (mA) 0.9 Quiescent Current (mA) 4.2 4.4 4.6 4.8 Input Voltage (V) Input Voltage (V) 0.85 0.8 0.75 0.7 0.65 0.6 0.55 3.25 3 2.75 2.5 2.25 2 1.75 1.5 1.25 1 0.5 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 Input Voltage (V) Input Voltage (V) Shutdown Current vs. Input Voltage x1 Mode Inrush Current Response 1.2 Shutdown Current (μA)1 4 5 VIN = 3.7V 1 EN (5V/Div) VOUT (2V/Div) 0.8 0.6 C2P (2V/Div) 0.4 0.2 IIN (200mA/Div) 0 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 Time (100μs/Div) Input Voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS9378-04 January 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT9378 x1.5 Mode Inrush Current Response EN (5V/Div) VOUT (2V/Div) VIN = 3.1V x2 Mode Inrush Current Response VIN = 2.8V EN (5V/Div) VOUT (2V/Div) C2P (2V/Div) C2P (2V/Div) IIN (200mA/Div) IIN (200mA/Div) Time (100μs/Div) Time (100μs/Div) x1 Mode Dimming Operation Ripple & Spike VIN (50mV/Div) EN (2V/Div) VOUT (20mV/Div) C2P (5V/Div) ILED (10mA/Div) VIN = 3.7V Time (1ms/Div) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 IIN (100mA/Div) VIN = 3.2V Time (1μs/Div) is a registered trademark of Richtek Technology Corporation. DS9378-04 January 2014 RT9378 Applications Information The RT9378 uses a fractional switched capacitor charge pump to power up to four white LEDs with a programmable current for uniform intensity. The part integrates current sources and automatic mode selection charge pump. It maintains the high efficiency by utilizing an x1/x1.5/x2 fractional charge pump and current sources. The small equivalent x1 mode open loop resistance and ultra-low dropout voltage of current source extend the operating time of x1 mode and optimize the efficiency in white LED applications. CFLY1 0.22µF VBAT 2.8V to 4.5V 3 C1P CFLY2 0.22µF 4 12 1 C1N C2P C2N 5 VIN CIN 1µF 6 PWM Dimming 2, Exposed pad (13) EN GND RT9378 LED1 LED2 LED3 LED4 VOUT 7 8 9 10 11 COUT 1µF Figure 1. Application Circuit for One Channel Disabled Input UVLO The input operating voltage range of the LED driver is from 2.8V to 4.5V. An input capacitor at the VIN pin could reduce ripple voltage. It is recommended to use a ceramic 1μF or larger capacitance as the input capacitor. This RT9378 provides an under voltage lockout (UVLO) function to prevent it from unstable issue when startup. The UVLO threshold of input rising voltage is set at 2V typically with a hysteresis of 100mV. Soft Start The charge pump employs a soft-start feature to limit the inrush current. The soft-start circuit prevents the excessive inrush current and input voltage droop. The soft-start clamps the input current over a typical period of 50μs. Mode Decision The RT9378 uses a smart mode selection method to decide the working mode for optimizing the efficiency. Mode decision circuit senses the output and LED voltage for up/down selection. The RT9378 automatically switches to x1.5 or x2 mode whenever the dropout condition is detected from the current source and returns to x1 mode whenever the dropout condition releases. LED connection The RT9378 supports up to 4 white LEDs. The 4 LEDs are connected from VIN to pin7, 8, 9, and 10 respectively. If the LED is not used, the LED pin should be connected to VIN directly. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS9378-04 January 2014 Capacitor Selection To get the better performance of the RT9378, the selection of peripherally appropriate capacitor and value is very important. These capacitors determine some parameters such as input/output ripple voltage, power efficiency and maximum supply current by charge pump. To reduce the input and output ripple effectively, the low ESR ceramic capacitors are recommended. 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 impedance. The flying capacitor CFLY1 and CFLY2 determine the supply current capability of the charge pump to influence the overall efficiency of the system. The lower value will improve efficiency. Howere, it will limit the LED’ s current at low input voltage. For 4 X25mA load over the entire input range of 2.8V to 4.5V, it is recommended to use a 0.22μF ceramic capacitor on the flying capacitor CFLY1 and CFLY2. Brightness Control The RT9378 implements a PWM dimming method to control the brightness of white LEDs. When an external PWM signal is connected to the EN pin, brightness of white LED is adjusted by the duty cycle. The suggest PWM dimming frequency is 1kHz to 4kHz and the PWM minimum turn on time must be >20μs. is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT9378 Thermal Considerations Layout Considerations For continuous operation, do not exceed absolute maximum operation junction temperature. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junction to ambient. The maximum power dissipation can be calculated by following formula : The RT9378 is a high-frequency switched-capacitor converter. Careful PCB layout is necessary. For best performance, place all peripheral components as close to the IC as possible. Place CIN, COUT, CFLY1, and CFLY2 near to VIN, VOUT, CP1, CN1, CP2, CN2, and GND pin respectively. A short connection is highly recommended. The following guidelines should be strictly followed when designing a PCB layout for the RT9378. PD(MAX) = ( TJ(MAX) − TA ) / θJA Where T J(MAX) is the maximum operation junction temperature, TA is the ambient temperature and the θJA is the junction to ambient thermal resistance. For recommended operating conditions specification of RT9378, The maximum junction temperature is 125°C. The junction to ambient thermal resistance θJA is layout dependent. For WQFN-12L 2x2 packages, the thermal resistance θJA is 165°C/W on the standard JEDEC 51-3 single layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by following formula : PD(MAX) = (125°C − 25°C) / (165°C/W) = 0.606W for WQFN-12L 2x2 packages The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance θJA. For RT9378 packages, the Figure 2 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed. Maximum Power Dissipation (W)1 0.8 ` The exposed GND pad must be soldered to a large ground plane for heat sinking and noise prevention. The throughhole vias located at the exposed pad is connected to ground plane of internal layer. ` VIN traces should be wide enough to minimize inductance and handle the high currents. The trace running from battery to chip should be placed carefully and shielded strictly. ` Input and output capacitors must be placed close to the part. The connection between pins and capacitor pads should be copper traces without any through-hole via connection. ` The flying capacitors must be placed close to the part. The traces running from the pins to the capacitor pads should be as wide as possible. Long traces will also produce large noise radiation caused by the large dv/dt on these pins. Short trace is recommended. ` All the traces of LED and VIN running from pins to LCM module should be shielded and isolated by ground plane. The shielding prevents the interference of high frequency noise coupled from the charge pump. ` Output capacitor must be placed between GND and VOUT to reduce noise coupling from charge pump to LEDs. Single Layer PCB 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 10 20 30 40 50 60 70 80 90 100 110 120 Ambient Temperature (°C) Figure 2. Derating Curves for RT9378 Packages Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS9378-04 January 2014 RT9378 Output capacitor (COUT) should be placed close to VOUT and connected to ground plane to reduce noise coupling from charge pump to LEDs. All the traces of LED pins running from chip to LEDs should be wide and short to reduce the parasitic connection resistance. C2N VOUT LED4 COUT 12 11 10 C1N GND C1P 9 1 GND 2 8 LED3 LED2 LED1 C2P VIN EN 13 The traces running 7 3 from pins to flying 4 5 6 capacitor should be short and wide to reduce parasitic Battery resistance and GND prevent noise CIN radiation. Input capacitor (CIN) should be placed close to V IN 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. Figure 2. PCB Layout for RT9378 Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS9378-04 January 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT9378 Outline Dimension 1 1 2 2 DETAIL A Pin #1 ID and Tie Bar Mark Options 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 0.150 0.250 0.006 0.010 D 1.900 2.100 0.075 0.083 E 1.900 2.100 0.075 0.083 e 0.400 0.016 D2 0.850 0.950 0.033 0.037 E2 0.850 0.950 0.033 0.037 L 0.250 0.350 0.010 0.014 W-Type 12L QFN 2x2 Package Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. www.richtek.com 10 DS9378-04 January 2014