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Features

 2.5V to 5.5V Input Voltage Range  36V Open LED Protection for 10 WLEDs  Pulse Dimming Brightness Control  200mV Reference Voltage with ±±±±±2% Accuracy  550kHz Switching Frequency  Built-In Soft-Start  Over-Temperature Protection  Internal Compensation RT4503/A Package Type QW : WDFN-6L 2x2 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) RT4503 : PWM Dimming RT4503A : Pulse Dimming LX FB GND RT4503/A VIN COMP* EN L VIN

www.richtek.com DS4503/A-03 June 2015 ©Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Functional Pin Description Pin No. Pin Name Pin Function 1 FB Feedback Voltage Input. Place a resistor between this pin and GND to set the current. COMP (RT4503) Connect an External Capacitor to this Pin. NC (RT4503A) No Internal Connection. 7 (Exposed Pad) GND Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum thermal dissipation. 4 LX Switch Node. Connect the pin to the switch side of the inductor. 5 EN Enable Control Input and Pulse Dimming Input. 6 VIN Supply Voltage Input. WDFN-6L 2x2 (TOP VIEW) FB NC VIN EN LXGND GND Pin Configurations RT4503 WDFN-6L 2x2 RT4503A FB COMP VIN EN LXGND GND Marking Information 1TW 1T : Product Code W : Date Code RT4503GQW 2R : Product Code W : Date Code RT4503AGQW 2RW

DS4503/A-03 June 2015 www.richtek.com ©Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Function Block Diagram Operation The RT4503/A is a constant frequency, current mode Boost LED driver. In normal operation, the N-MOSFET is turned on when the PWM Control circuit is set by the oscillator and is turned off when the current comparator resets the PWM Control circuit. While the N-MOSFET is turned off, the inductor current conducts through the external diode. UVLO When the input voltage is lower than the UVLO threshold (2.37V typ.), the driver will turn off. There is a 80mV for the UVLO hysteresis control. Soft-Start When the device is enabled, the Comp ramps up to the target voltage in a specific time. This ensures that the output voltage rises slowly to reduce the input inrush current. EN Dimming The EN pin is used for the control input for both PWM dimming mode and digital dimming mode. Shutdown delay when the EN voltage is logic low for more than specific time, the driver will be shut down. OCP The driver provides cycle-by-cycle current limit function to control the current on power switch. OVP The over-voltage protection function monitors the output voltage via the LX pin voltage. The OVP threshold voltage is 36V typically. Once the LED is open, the output voltage reaches the OVP threshold, the driver will be shut down. OTP The over-temperature protection function will shut down the switching operation when the junction temperature exceeds 160 °C. Once the junction temperature cools down by approximately 15 °C, the converter will automatically resume switching. FB OVP ISENSE OCP Back Light PWM Logic IBIASOTP UVLO Control Logic OSC Slope Internal Compensation VREF Dimming DAC + - + EA GND LX COMP EN VIN (RT4503)

www.richtek.com DS4503/A-03 June 2015 ©Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation.

Electrical Characteristics

Recommended Operating Conditions (Note 4) (VIN = 3.6V, CIN = 2.2μF, COUT = 1μF, L = 22μH, fSW = 550kHz, TA = 25°C, unless otherwise specified) Absolute Maximum Ratings (Note 1)  Power Dissipation, PD @ TA = 25°C  Package Thermal Resistance (Note 2)  ESD Susceptibility (Note 3) Parameter Symbol Test Conditions Min Typ Max Unit Power Supply IC Operating Current (switching) I Q_SW V FB = 0V 0.25 0.8 1.5 mA IC Quiescent Current (non-switching) I Q V FB = 0.4V 0.25 0.35 0.5 mA VIN Pin Shutdown Current I SHDN EN = GND -- 0.3 1 A Under-Voltage Lockout Threshold UVLO VIN Rising Edge 2.25 2.37 2.5 V Under-Voltage Lockout Hysteresis U VLO_hys VIN Falling Edge -- 80 -- mV Enable and Reference Control EN Input Voltage Logic-High V IH 1.4 -- -- V Logic-Low V IL -- -- 0.4 EN Pull Low Resistance R EN -- 300 -- k  EN minimum Shut down Pulse Width Toff For RT4503 20 -- -- ms Toff For RT4503A 2 -- -- ms EN Minimum Logic High Pulse Width T High_MIN 0.5 -- -- s EN Minimum Logic Low Pulse Width T Low 0.5 -- 1000 s Internal Comp Resistance R comp -- 120 -- k  PWM Minimum Duty without IC Shutdown DPWM MIN For RT4503, V FB > 0mV 1 -- -- % PWM Frequency f PW M For RT4503 1 -- 100 kHz

DS4503/A-03 June 2015 www.richtek.com ©Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Note 1. Stresses beyond those listed “Absolute Maximum Ratings ” may cause permanent damage to the device. These are stress ratings only, and 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 may affect device reliability. Note 2. θ JA is measured at T A = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. First EN pulse for pulse dimming see Timing Diagram. Parameter Symbol Test Conditions Min Typ Max Unit Voltage and Current Control Feedback Regulation Voltage V FB 196 200 204 mV Feedback Pin Bias Current I FB -- -- 0.1 A Oscillator Frequency f SW 495 550 605 kHz Maximum Duty Cycle D MAX -- 93 -- % Power Switch N-MOSFET On-Resistance R DS(ON) V IN = 3.6V -- 0.4 0.7  OC and OLP Peak N-MOSFET Current Limit I LIM 1 1.2 1.4 A Open LED Protection Threshold OVP 35 36.5 38 V Thermal Shutdown Thermal Shutdown Threshold T SD -- 160 -- °C Thermal Shutdown Hysteresis TSD -- 15 -- °C

www.richtek.com DS4503/A-03 June 2015 ©Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Typical Application Circuit Timing Diagram * : COMP pin for RT4503 only, the 220nF capacitor is suitable for most applications. THIGH EN ILED TS TLOW 50µs TOFF Off 31/3230/32 29/3228/3227/32 26/32 LX FB GND RT4503/A VIN COMP* EN 2.2µF L 22µH 1µF Up to 36V VIN 2.5V to 5.5V

DS4503/A-03 June 2015 www.richtek.com ©Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Oscillator Frequency vs. Input Voltage 558 560 562 564 566 568 570 572 574 576 578 580 582 584 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) Frequency (kHz) 1 Typical Operating Characteristics Quiescent Current vs. Temperature 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 -50 -25 0 25 50 75 100 125 Temperature (°C) Quiescent Current (mA ) Switching Quiescent Current Non-Switching Quiescent Current Efficiency vs. Output Current 100 Output Current (A) Efficiency (%) VOUT = 30V VIN = 3.3V VIN = 3.7V VIN = 4.2V VIN = 5.5V Quiescent Current vs. Input Voltage 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) Quiescent Current (mA ) Switching Quiescent Current Oscillator Frequency vs. Temperature 450 470 490 510 530 550 570 590 610 630 650 -50 -25 0 25 50 75 100 125 Temperature (°C) Frequency (kHz) 1 Efficiency vs. Input Voltage 100 Input Voltage (V) Efficiency (%) VOUT = 30V Load = 20mA Load = 30mA

www.richtek.com DS4503/A-03 June 2015 ©Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Reference Voltage vs. Pulse Dimming Step 100 120 140 160 180 200 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 Pulse Dimming Step Reference Voltage (mV) VIN Shutdown Current vs. Input Voltage 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) Shutdown Current (µA) 1 Open LED Protection vs. Input Voltage 34.0 34.5 35.0 35.5 36.0 36.5 37.0 37.5 38.0 38.5 39.0 Input Voltage(V) OVP (V) Reference Voltage vs. Input Voltage 190 192 194 196 198 200 202 204 206 208 210 0 3 6 9 12 15 18 21 24 27 30 Output Current (mA) Reference Voltage (mV) VIN = 5.5V VIN = 4.2V VIN = 3.7V Reference Voltage vs. Output Current 194.0 196.2 198.4 200.6 202.8 205.0 0 3 6 9 12 15 18 21 24 27 30 Output Current (mA) Reference Voltage (mV) VIN = 5.5V VIN = 4.2V VIN = 3.7V Reference Voltage vs. PWM Dimming Duty Cycle 100 150 200 250 0 2 04 06 08 0 1 0 0 PWM dimming Duty Cycle (%) Reference Voltage (mV) 10kHz

DS4503/A-03 June 2015 www.richtek.com ©Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Time (5 μs/Div) PWM Dimming VIN = 3.7V, F = 50kHz, Duty = 50% ILED (10mA/Div) EN (2V/Div) VOUT (100mV/Div) FB (20mV/Div) Time (5ms/Div) Pulse Dimming VIN = 3.7V, IOUT = 20mA to 10mA ILED (10mA/Div) EN (1V/Div) Time (5ms/Div) Pulse Dimming ILED (10mA/Div) EN (1V/Div) VIN = 3.7V, IOUT = 20mA to zero VIN = 3.7V Time (25ms/Div) Power On from EN IIN (200mA/Div) EN (2V/Div) VOUT (10V/Div) COMP (100mV/Div) VIN = 3.7V Time (5ms/Div) Power Off from EN IIN (200mA/Div) EN (2V/Div) LX (20V/Div) VOUT (10V/Div) Time (250 μs/Div) PWM Dimming VIN = 3.7V, F = 1kHz, Duty = 50% ILED (10mA/Div) EN (2V/Div) VOUT (500mV/Div) FB (20mV/Div)

www.richtek.com DS4503/A-03 June 2015 ©Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation.

Application Information

The RT4503/A includes a soft-start function to avoid high inrush current during start-up. The soft-start function is achieved by clamping the output voltage of the error amplifier with another voltage source that is increased slowly from zero to near VIN. LED Current The loop control of the Boost converter keeps V FB equal to a reference voltage, V REF. Therefore, when R SET is connected between the FB pin and GND, the LED current will be determined by the current through R SET, which is equal to VFB / RSET. Current Limit The current flowing through the inductor during a charging period is detected by a current sensing circuit. If the value exceeds the current limit, the N-MOSFET will be turned off. The inductor will then be forced to leave charging stage and enter discharging stage. Therefore, the inductor current will not increase to reach current limit. Shutdown Delay When the EN voltage is in logic low for 20ms during PWM dimming for RT4503 and 2ms during pulse dimming for RT4503A, the system will enter shutdown. FB REFV = D u t y V Where : Duty = duty cycle of the PWM signal V REF = internal reference voltage (200mV typ.) The RT4503 chops up the internal 200mV reference voltage via the duty cycle of the PWM signal. Therefore, although a PWM signal is used for brightness dimming, only the LED DC current is modulated, which is often referred as analog dimming. This eliminates the audible noise which often occurs when the LED current is pulsed in replica of the frequency and duty cycle of PWM control. For optimum performance, use the PWM dimming frequency in the range of 1kHz to 100kHz. PWM Dimming When the EN pin is constantly high, the FB voltage is regulated to 200mV typically. The RT4503 allows a PWM signal from EN pin to reduce the regulation voltage; and achieve LED brightness dimming. The relationship between the duty cycle and FB voltage is given by FB Duty1 x 200mV 1kHz < fPWM < 100kHz Duty2 Duty1 Duty2 x 200mV TSHDN > 20ms EN Period1 Period2

DS4503/A-03 June 2015 www.richtek.com ©Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Pulse Dimming The EN pin features a simple digital interface to allow digital brightness control. Using the digital interface to control the LED brightness does not require a PWM signal. 1 2 3 4 567 89 THI 40µs TSHDN > 2ms CTRL FB 0.5µs < TLO < 1000µs0.5µs < THi 200mV (23/32) x 200mV The digital brightness control is implemented by adjusting the feedback voltage in digital steps with a typical maximum voltage of V FB = 200mV. For this purpose, a 5- bit DAC is used to display 32 steps equaling to a 6.25mV change in feedback voltage per step. Inductor Selection The recommended value of inductor for 10 LEDs or high brightness LED applications is 22 μH. Smaller size and better efficiency are the major concerns for portable devices. The inductor should have low core loss at 550kHz and low DCR for better efficiency. The inductor saturation current rating should be considered to cover the inductor peak current. Capacitor Selection For low ripple voltage, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of their wide voltage range and good operating temperature characteristics. For the application of the RT4503/A to drive 10 LEDs in series, a 2.2 μF for input capacitor, a 1μF for output capacitor. Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : P D(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WDFN-6L 2x2 package, the thermal resistance, θJA, is 47.5°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : PD(MAX) = (125 °C − 25 °C) / (47.5 °C/W) = 2.1W for WDFN-6L 2x2 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 1 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation.

DS4503/A-03 June 2015 www.richtek.com 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 furnish ed 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 infringeme nts 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 R ichtek or its subsidiaries. Outline Dimension Dimensions In Millimeters Dimensions In Inches Symbol 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 0.200 0.350 0.008 0.014 D 1.950 2.050 0.077 0.081 D2 1.000 1.450 0.039 0.057 E 1.950 2.050 0.077 0.081 E2 0.500 0.850 0.020 0.033 e 0.650 0.026 L 0.300 0.400 0.012 0.016 W-Type 6L DFN 2x2 Package D E A e b L SEE DETAIL A 1 122 Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. DETAIL A Pin #1 ID and Tie Bar Mark Options