® RT4503/A Asynchronous Boost Converter for 10 WLEDs General Description Features The RT4503/A is a highly integrated LED driver IC capable of driving 10 WLEDs in series. It is composed of a current mode Boost converter integrated with a 36V/1.2A power switch. 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 Current Limit The RT4503/A supports a wide input voltage range from 2.5V to 5.5V and runs at a fixed frequency of 550kHz. The LED current is set via an external resistor and the feedback voltage is regulated to 200mV. For brightness dimming, the RT4503A supports 32 steps pulse dimming which determines the feedback reference voltage, and RT4503 support PWM dimming which determines the feedback reference voltage. Ordering Information RT4503/A Package Type QW : WDFN-6L 2x2 (W-Type) Applications Lead Plating System G : Green (Halogen Free and Pb Free) Cellular Phones Digital Cameras Probable Instruments RT4503 : PWM Dimming RT4503A : Pulse Dimming Note : 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. Simplified Application Circuit L LX VIN VIN … RT4503/A EN GND COMP* FB * : COMP pin for RT4503 only. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4503/A-03 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT4503/A Pin Configurations Marking Information (TOP VIEW) RT4503GQW W : Date Code 1TW FB 1 COMP GND 2 GND 1T : Product Code 3 7 6 VIN 5 EN LX 4 WDFN-6L 2x2 RT4503AGQW RT4503 2R : Product Code FB 1 NC GND 2 GND W : Date Code 2RW 3 7 6 VIN 5 EN LX 4 WDFN-6L 2x2 RT4503A Functional Pin Description Pin No. 1 2 Pin Name FB Pin Function 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) 3, GND 7 (Exposed Pad) No Internal Connection. 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. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS4503/A-03 June 2015 RT4503/A Function Block Diagram COMP (RT4503) VREF Dimming DAC FB Internal Compensation OVP LX + EA - Back Light PWM Logic + - Slope OSC ISENSE GND EN VIN Control Logic OTP IBIAS UVLO OCP 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. 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. 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. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4503/A-03 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT4503/A Absolute Maximum Ratings (Note 1) VIN ---------------------------------------------------------------------------------------------------------------------EN, FB, COMP to GND -------------------------------------------------------------------------------------------LX to GND ------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WDFN-6L 2x2 -------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WDFN-6L 2x2, θJA --------------------------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------------- Recommended Operating Conditions −0.3V to 6V −0.3V to (VIN + 0.3V) −0.3V to 38V 2.1W 47.5°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VIN ------------------------------------------------------------------------------------------ 2.5V to 5.5V Junction Temperature Range -------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 3.6V, CIN = 2.2μF, COUT = 1μF, L = 22μH, fSW = 550kHz, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Power Supply IC Operating Current (switching) IQ_SW VFB = 0V 0.25 0.8 1.5 mA IC Quiescent Current (non-switching) IQ VFB = 0.4V 0.25 0.35 0.5 mA VIN Pin Shutdown Current ISHDN 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 UVLO_hys VIN Falling Edge -- 80 -- mV Enable and Reference Control EN Input Voltage Logic-High VIH 1.4 -- -- Logic-Low VIL -- -- 0.4 REN -- 300 -- k EN Pull Low Resistance EN minimum Shut down Pulse Width V Toff For RT4503 20 -- -- ms Toff For RT4503A 2 -- -- ms EN Minimum Logic High Pulse Width THigh_MIN 0.5 -- -- s EN Minimum Logic Low Pulse Width TLow 0.5 -- 1000 s Internal Comp Resistance PWM Minimum Duty without IC Shutdown PWM Frequency Rcomp -- 120 -- k DPWM MIN For RT4503, VFB > 0mV 1 -- -- % f PWM 1 -- 100 kHz Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 For RT4503 is a registered trademark of Richtek Technology Corporation. DS4503/A-03 June 2015 RT4503/A Parameter Symbol Test Conditions Min Typ Max Unit Voltage and Current Control Feedback Regulation Voltage VFB 196 200 204 mV Feedback Pin Bias Current IFB -- -- 0.1 A Oscillator Frequency f SW 495 550 605 kHz Maximum Duty Cycle DMAX -- 93 -- % -- 0.4 0.7 Power Switch N-MOSFET On-Resistance RDS(ON) VIN = 3.6V OC and OLP Peak N-MOSFET Current Limit ILIM 1 1.2 1.4 A Open LED Protection Threshold OVP 35 36.5 38 V Thermal Shutdown Threshold TSD -- 160 -- °C Thermal Shutdown Hysteresis TSD -- 15 -- °C Thermal Shutdown 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. θJA is measured at TA = 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. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4503/A-03 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT4503/A Typical Application Circuit L 22µH Up to 36V 1µF LX VIN 2.5V to 5.5V VIN 2.2µF … RT4503/A EN GND COMP* FB * : COMP pin for RT4503 only, the 220nF capacitor is suitable for most applications. Timing Diagram THIGH TOFF EN 50µs TS TLOW 31/3230/32 29/3228/32 27/32 26/32 ILED Off Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS4503/A-03 June 2015 RT4503/A Typical Operating Characteristics Efficiency vs. Output Current Efficiency vs. Input Voltage 100 100 90 90 80 VIN = VIN = VIN = VIN = 70 60 3.3V 3.7V 4.2V 5.5V Efficiency (%) Efficiency (%) 80 50 40 30 20 Load = 20mA Load = 30mA 70 60 50 40 30 20 10 10 VOUT = 30V 0 VOUT = 30V 0 0 0.005 0.01 0.015 0.02 0.025 0.03 2.5 2.8 3.1 3.4 Output Current (A) 4 4.3 4.6 4.9 5.2 5.5 Input Voltage (V) Quiescent Current vs. Input Voltage Quiescent Current vs. Temperature 0.80 0.7 0.75 0.6 Quiescent Current (mA) Quiescent Current (mA) 3.7 0.70 0.65 0.60 0.55 0.50 Switching Quiescent Current 0.5 0.4 Non-Switching Quiescent Current 0.3 0.2 0.1 Switching Quiescent Current 0.45 0.0 2.5 3 3.5 4 4.5 5 5.5 -50 -25 0 Oscillator Frequency vs. Input Voltage 50 75 100 125 Oscillator Frequency vs. Temperature 650 584 582 580 578 576 574 572 570 568 566 564 562 560 558 630 610 Frequency (kHz)1 Frequency (kHz)1 25 Temperature (°C) Input Voltage (V) 590 570 550 530 510 490 470 450 2.5 3 3.5 4 4.5 5 Input Voltage (V) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4503/A-03 June 2015 5.5 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT4503/A Reference Voltage vs. Output Current Reference Voltage vs. Input Voltage 205.0 210 Reference Voltage (mV) Reference Voltage (mV) 208 206 204 202 200 VIN = 5.5V VIN = 4.2V VIN = 3.7V 198 196 194 202.8 200.6 VIN = 5.5V VIN = 4.2V VIN = 3.7V 198.4 196.2 192 194.0 190 0 3 6 9 12 15 18 21 24 27 0 30 3 6 9 12 15 18 21 24 27 30 Output Current (mA) Output Current (mA) Reference Voltage vs. Pulse Dimming Step Reference Voltage vs. PWM Dimming Duty Cycle 200 250 Reference Voltage (mV) Reference Voltage (mV) 180 160 140 120 100 80 60 40 200 150 100 50 20 10kHz 0 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 0 20 Pulse Dimming Step VIN Shutdown Current vs. Input Voltage 60 80 100 Open LED Protection vs. Input Voltage 0.35 39.0 38.5 0.30 38.0 0.25 37.5 OVP (V) Shutdown Current (µA)1 40 PWM dimming Duty Cycle (%) 0.20 0.15 37.0 36.5 36.0 35.5 0.10 35.0 0.05 34.5 0.00 34.0 2.5 3 3.5 4 4.5 5 Input Voltage (V) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 5.5 2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5 Input Voltage(V) is a registered trademark of Richtek Technology Corporation. DS4503/A-03 June 2015 RT4503/A Power On from EN Power Off from EN EN (2V/Div) EN (2V/Div) VOUT (10V/Div) COMP (100mV/Div) VOUT (10V/Div) LX (20V/Div) I IN (200mA/Div) I IN (200mA/Div) VIN = 3.7V VIN = 3.7V Time (25ms/Div) Time (5ms/Div) PWM Dimming PWM Dimming EN (2V/Div) EN (2V/Div) VOUT (500mV/Div) VOUT (100mV/Div) FB (20mV/Div) FB (20mV/Div) I LED (10mA/Div) I LED (10mA/Div) VIN = 3.7V, F = 50kHz, Duty = 50% VIN = 3.7V, F = 1kHz, Duty = 50% Time (250μs/Div) Time (5μs/Div) Pulse Dimming Pulse Dimming EN (1V/Div) EN (1V/Div) I LED (10mA/Div) I LED (10mA/Div) VIN = 3.7V, IOUT = 20mA to zero Time (5ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4503/A-03 June 2015 VIN = 3.7V, IOUT = 20mA to 10mA Time (5ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT4503/A Application Information Soft-Start PWM Dimming 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. 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 LED Current VFB = Duty VREF The loop control of the Boost converter keeps VFB equal Where : to a reference voltage, VREF. Therefore, when RSET is connected between the FB pin and GND, the LED current will be determined by the current through RSET, which is equal to VFB / RSET. Duty = duty cycle of the PWM signal 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. VREF = 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. 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. Period1 EN Duty1 Period2 1kHz < fPWM < 100kHz TSHDN > 20ms Duty2 Duty1 x 200mV Duty2 x 200mV FB Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS4503/A-03 June 2015 RT4503/A The digital brightness control is implemented by adjusting the feedback voltage in digital steps with a typical maximum voltage of VFB = 200mV. For this purpose, a 5bit DAC is used to display 32 steps equaling to a 6.25mV change in feedback voltage per step. 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. 0.5µs < THi THI 40µs 0.5µs < TLO < 1000µs TSHDN > 2ms CTRL 0 1 2 3 4 5 6 7 8 9 0 200mV (23/32) x 200mV 0 FB Inductor Selection The recommended value of inductor for 10 LEDs or high brightness LED applications is 22μH. 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 2.2μF 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 Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4503/A-03 June 2015 maximum power dissipation can be calculated by the following formula : PD(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. is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT4503/A Layout Consideration Maximum Power Dissipation (W)1 2.5 For best performance of the RT4503/A, the following guide lines must be strictly followed. Four-Layer PCB 2.0 Input and Output capacitors should be placed close to the IC and connected to ground plane to reduce noise coupling. The GND and Exposed Pad should be connected to a strong ground plane for heat sinking and noise protection. Keep the main current traces as possible as short and wide. 125 LX node of DC/DC converter is with high frequency voltage swing. It should be kept at a small area. Figure 1. Derating Curve of Maximum Power Dissipation Place the feedback components as close as possible to the IC and keep away from the noisy devices. 1.5 1.0 0.5 0.0 0 25 50 75 100 Ambient Temperature (°C) FB node copper area should be minimized and keep far away from noise sources (LX pin) and RSET should be as close as possible to FB pin. GND ... CCOMP FB 1 COMP GND 2 GND RSET 3 7 6 5 4 CIN VIN EN LX COUT VOUT Output capacitor must be placed between GND and VOUT to reduce noise. Input capacitor must close to VIN to reduce noise. The inductor should be placed as close as possible to the switch pin to minimize the noise coupling into other circuits. LX node copper area should be minimized for reducing EMI. Figure 2. PCB Layout Guide Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS4503/A-03 June 2015 RT4503/A Outline Dimension D2 D L E E2 1 e b A A1 SEE DETAIL A 2 1 2 1 A3 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. 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 L 0.650 0.300 0.026 0.400 0.012 0.016 W-Type 6L DFN 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. DS4503/A-03 June 2015 www.richtek.com 13