RT9284A/B Tiny Package, High Performance, Constant Current Switching Regulator for White LED General Description Features The RT9284A/B is a compact, high efficient and high integration LED driver. Internal 22V MOSFET can support 2 to 5 White LEDs for backlighting and camera flashing. z Highly integration and internal compensation network minimizes as 5 external component counts. Optimized operation frequency can meet the requirement of small LC filters value and low operation current with high efficiency. Internal soft start function can reduce the inrush current. Tiny package type of TSOT-23-5 and TSOT-23-6 packages provide the best solution for PCB space saving and total BOM cost. z z z z z z z z z VIN Operating Range : 2.7V to 5.5V Maximum Output Voltage up to 20V Dimming with Zero-inrush and Wide Frequency Range Over Voltage Protection Output Current up to 100mA at VOUT = 12V. Zero Shutdown Supply Current Minimize the External Component Small LC Filter Internal Soft Start RoHS Compliant and 100% Lead (Pb)-Free Ordering Information Applications RT9284 (- z ) E Package Type J5 : TSOT-23-5 J6 : TSOT-23-6 z z z Camera Flash White LED Mobile Phone, Smart Phone LED Backlight PDA LED Backlight Digital Still Camera Camcorder Operating Temperature Range z P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) Pin Configurations TOP VIEW OVP Voltage 15 : 15V 20 : 20V FB Voltage A : 1.235V B : 0.25V Note : RichTek Pb-free and Green products are : EN 5 4 1 2 3 LX GND FB TSOT-23-5 `RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. VDD OVP `Suitable for use in SnPb or Pb-free soldering processes. `100% matte tin (Sn) plating. Marking Information For marking information, contact our sales representative directly or through a RichTek distributor located in your area, otherwise visit our website for detail. VDD EN 6 5 4 1 2 3 LX GND FB TSOT-23-6 Note : There is no pin1 indicator on top mark for TSOT-23-6 type, and pin 1 will be lower left pin when reading top mark from left to right. DS9284A/B_E-02 August 2006 www.richtek.com 1 RT9284A/B Typical Application Circuit D1 SS0520 L1 4.7uH to 22uH VIN + 2.7V to 5.5V C1 1uF 2 EN GND OVP ILED C2 1uF/16V RT9284 6 1 VDD LX 4 Dimming Control OVP 15V C3 1uF 5 FB 3 R1 Figure 1. Application for Driving 3 Series WLEDs D1 SS0520 L1 4.7uH to 22uH VIN + 2.7V to 5.5V C1 1uF 2 EN GND OVP C2 1uF/25V R2 600k RT9284 6 1 VDD LX 4 Dimming Control OVP 18V ILED C3 1uF 5 OVP 15V FB 3 R1 Figure 2. Application for Driving 4 Series WLEDs D1 SS0520 L1 4.7uH to 22uH VIN + 2.7V to 5.5V C1 1uF C2 1uF/25V RT9284B 6 1 LX VDD 4 Dimming Control OVP 20V 2 EN GND OVP ILED C3 1uF 5 FB 3 VFB = 0.25V (typ.) R1 Figure 3. Application for Driving 5 Series WLEDs D1 OVP SS0520 15V L1 4.7uH to 22uH VIN + 2.7V to 5.5V C1 1uF VOUT = R1 + R2 × VFB R2 VFB = 1.235 (typ.) R2 > 100k Ω RT9284A 6 1 LX VDD 4 2 EN GND OVP VOUT 12V R1 910k C2 1uF/16V 5 FB 3 VFB = 1.235V (typ.) R2 105k Figure 4. Application for Constant Output Voltage www.richtek.com 2 DS9284A/B_E-02 August 2006 RT9284A/B Pin Description TSOT-23-5 TSOT-23-6 Pin Name Pin Function 1 1 LX Switch Pin. Connect this Pin to inductor and catch diode. Minimize the track area to reduce EMI. 2 2 GND Ground Pin 3 3 FB Feedback Reference Voltage Pin. Series connect a resistor between WLED and ground as a current sense. Sense the current feedback voltage to set the current rating. 4 4 EN Chip Enable (Active High). Voltage sensing input to trigger the function of over voltage protection. Note that this pin is high impedance. There should be a pull low 100kΩ resistor connected to GND when the control signal is floating. -- 5 OVP Over Voltage Protection Pin. Voltage sensing input to trigger the function of over voltage protection. Leave it unconnected to disable this function. 5 6 VDD Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input noise. Function Block Diagram 1.2MHz OSC VDD Current Bias BandGap ibias OCP 750mA PWM Logic VREF LX Protection Circuit OVP OVP + - UVLO Buffer EN DS9284A/B_E-02 August 2006 Timer 2.5ms FB + VREF GND Soft Start www.richtek.com 3 RT9284A/B Absolute Maximum Ratings z z z z z z z z z z (Note 1) Supply Input Voltage -------------------------------------------------------------------------------------------------- −0.3V to 7V LX Input Voltage ------------------------------------------------------------------------------------------------------- −0.3V to 22V OVP Voltage ------------------------------------------------------------------------------------------------------------ −0.3V to 22V The Other Pins --------------------------------------------------------------------------------------------------------- −0.3V to 6V Power Dissipation, PD @ TA = 25°C TSOT-23-5 --------------------------------------------------------------------------------------------------------------- 0.455W TSOT-23-6 --------------------------------------------------------------------------------------------------------------- 0.455W Package Thermal Resistance (Note 4) TSOT-23-5, θJA --------------------------------------------------------------------------------------------------------- 220°C/W TSOT-23-6, θJA --------------------------------------------------------------------------------------------------------- 220°C/W Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260°C Junction Temperature ------------------------------------------------------------------------------------------------- 150°C Storage Temperature Range ---------------------------------------------------------------------------------------- −65°C to 150°C ESD Susceptibility (Note 2) HBM (Human Body Mode) ------------------------------------------------------------------------------------------ 2kV MM (Machine Mode) -------------------------------------------------------------------------------------------------- 200V Recommended Operating Conditions z z (Note 3) Junction Temperature Range ---------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range ---------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 3.7V, TA = 25°C unless otherwise specified) Parameter Symbol Test Condition Min Typ Max Units System Supply Input Operation Voltage Range VDD 2.7 -- 5.5 V Under Voltage Lock Out VDD 1.8 2.2 2.5 V Quiescent Current IDD FB = 1.5V, No switch 50 300 1000 uA Supply Current IDD FB = 0V, Switch 0.1 2 3 mA Shut Down Current IDD VEN < 0.4V -- -- 1 uA VIN = 3.0 to 4.3V -- 3 -- % 0.9 1.2 1.5 MHz 85 -- -- % RT9284A 1.173 1.235 1.296 V RT9284B 0.237 0.25 0.263 V Line Regulation Oscillator Operation Frequency fOSC Maximum Duty Cycle Reference Voltage Feedback Voltage (Note 5) To be continued www.richtek.com 4 DS9284A/B_E-02 August 2006 RT9284A/B Parameter Symbol Test Condition Min Typ Max Units -- 0.75 -- Ω for 2,3,4 WLEDs application 14 15 16 V for 5 WLEDs application 19 20 21 V OVP Sink Current -- 5 -- μA OCP -- 750 -- mA MOSFET On Resistance of MOSFET RDS(ON) Protection OVP Threshold VOVP Shut Down Voltage VEN -- -- 0.4 V Enable Voltage VEN 1.5 -- -- V 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. Devices are ESD sensitive. Handling precaution recommended. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. 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 5. Floating the OVP pin to disable OVP function. DS9284A/B_E-02 August 2006 www.richtek.com 5 RT9284A/B Typical Operating Characteristics Enable Voltage vs. Input Voltage Shut Down Voltage vs. Input Voltage 1.2 1.2 -45°C 1.1 Shut Down Voltage (V) Enable Voltage (V) 1.1 1.0 25°C 0.9 85°C 0.8 0.7 0.6 -45°C 1 0.9 25°C 0.8 85°C 0.7 0.6 0.5 0.5 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 3 Efficiency vs. Input Voltage 4.25 4.5 4.75 5 5.25 5.5 LED Current vs. Input Voltage 22 84 ILED = 20mA, L = 4.7μH, DCR = 0.15Ω 4WLEDs, L = 10μH 21.5 83.5 LED Current (mA) 3WLEDs 83 Efficiency (%) 4 Input Voltage (V) Input Voltage (V) 82.5 4WLEDs 82 81.5 81 21 20.5 20 19.5 19 18.5 18 80.5 3 3.2 3.4 3.6 3.8 4 4.2 3 4.4 Input Voltage (V) 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 Input Voltage (V) Maximum Duty Cycle vs. VDD POR (Rising/Falling) vs. Temperature 91% 91 2.7 90% 90 2.5 89% 89 2.3 POR (V) Maximum Duty Cycle (%) 3.25 3.5 3.75 88% 88 2.1 87 87% 1.9 86 86% 1.7 85 85% Rising Falling 1.5 3 3.25 3.5 3.75 4 4.25 4.5 4.75 VDD (V) www.richtek.com 6 5 5.25 5.5 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 Temperature (°C) DS9284A/B_E-02 August 2006 RT9284A/B Switching Frequency vs. Temperature Switching Current vs. Input Voltage 1.5 Switching Current (mA) 1.8 -45°C 25°C 1.6 1.4 85°C 1.2 1 0.8 0.6 0.4 0.2 Switching Frequency (MHz) 2 1.45 1.4 1.35 1.3 1.25 1.2 1.15 1.1 1.05 0 1 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 Input Voltage (V) Temperature (°C) Feedback Voltage vs. Temperature Dimming Operation 252.2 4WLEDs, VIN = 3.7V, ILED = 20mA, L = 10μH Feedback Voltage (mV) 252 EN 251.8 (5V/Div) 251.6 I IN 251.4 (50mA/Div) 251.2 251 250.8 I LED (10mA/Div) f = 100Hz, Duty = 50% 250.6 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 Time (2ms/Div) Temperature (°C) Dimming Operation Dimming Operation 4WLEDs, VIN = 3.7V, ILED = 20mA, L = 10μH EN 4WLEDs, VIN = 3.7V, ILED = 20mA, L = 10μH EN (5V/Div) (5V/Div) I IN I IN (100mA/Div) (100mA/Div) (10mA/Div) I LED I LED (10mA/Div) f = 1kHz, Duty = 50% Time (400μs/Div) DS9284A/B_E-02 August 2006 f = 10kHz, Duty = 50% Time (40μs/Div) www.richtek.com 7 RT9284A/B OCP Dimming Operation L = 10μH 4WLEDs, VIN = 3.7V, ILED = 20mA, L = 10μH EN (10V/Div) (5V/Div) VOUT I IN ILX (100mA/Div) (500mA/Div) (10mA/Div) I LED LX (20V/Div) f = 100kHz, Duty = 50% Time (4μs/Div) Time (25μs/Div) Inrush Current Inrush Current 4WLEDs, VIN = 3.0V, ILED = 20mA, L = 4.7μH EN 4WLEDs, VIN = 4.3V, ILED = 20mA, L = 4.7μH (2V/Div) (2V/Div) EN (2V/Div) (2V/Div) VIN (5V/Div) (5V/Div) VIN VOUT VOUT I IN I IN (100mA/Div) (5V/Div) (100mA/Div) Time (500μs/Div) Time (500μs/Div) Normal Operation Normal Operation (5V/Div) 4WLEDs, VIN = 3.0V ILED = 20mA, L = 10μH 4WLEDs, VIN = 3.7V ILED = 20mA, L = 10μH (2V/Div) (2V/Div) VOUT VOUT (10V/Div) VIN VIN LX LX I IN (10V/Div) I IN (100mA/Div) (100mA/Div) Time (400ns/Div) www.richtek.com 8 Time (400ns/Div) DS9284A/B_E-02 August 2006 RT9284A/B Normal Operation Normal Operation (5V/Div) (5V/Div) (2V/Div) (2V/Div) VOUT 4WLEDs, VIN = 4.3V ILED = 20mA, L = 10μH (10V/Div) VOUT VIN VIN LX LX I IN 4WLEDs, VIN = 5.5V ILED = 20mA, L = 10μH (10V/Div) I IN (100mA/Div) (100mA/Div) Time (400ns/Div) DS9284A/B_E-02 August 2006 Time (400ns/Div) www.richtek.com 9 RT9284A/B Application Information C1 1uF D1 OVP SS0520 15V L1 4.7uH to 22uH LED Current Control The RT9284A/B regulates the LED current by setting the current sense resistor (R1) connecting to feedback and ground. As shown in Table 1, the RT9284A feedback voltage (VFB) is 1.235V and the RT9284B feedback voltage (VFB) is 0.25V. The LED current (ILED) can be set by a resistor R1. In order to have an accurate LED current, a precision resistor is preferred (1% is recommended). 6 4 VIN + 2 2.7V to 5.5V VDD EN GND LX OVP 1 5 R2 10k FB 3 R3 13k R1 110 VDC Dimming 0V to 2.8V Table 1 Feedback Reference LED Current Voltage VFB (V) Setting ILED (A) RT9284A 1.235 ILED = 1.235/R1 RT9284B 0.25 ILED = 0.25/R1 Version ILED C2 1uF/16V RT9284A Dimming Control a. Using a PWM Signal to EN Pin For controlling the LED brightness, the RT9284A/B can perform the dimming control by applying a PWM signal to EN pin. The internal soft start and the wide range dimming frequency can eliminate inrush current and audio noise when dimming. The average LED current is proportional to the PWM signal duty cycle. The magnitude of the PWM signal should be higher than the maximum enable voltage of EN pin, in order to let the dimming control perform correctly for preventing the flicker issue, the suqqested PWM frequency is ≥ 1kHz or ≤ 200Hz. Figure 5. Dimming Control Using a DC Voltage for RT9284A c. Using a Filtered PWM signal : Another common application is using a filtered PWM signal as an adjustable DC voltage for LED dimming control. A filtered PWM signal acts as the DC voltage to regulate the output current. The recommended application circuit is shown in the Figure 6. In this circuit, the output ripple depends on the frequency of PWM signal. For smaller output voltage ripple (<100mV), the recommended frequency of 2.8V PWM signal should be above 2kHz. To fix the frequency of PWM signal and change the duty cycle of PWM signal can get different output current as Figure 7. According to the application circuit of Figure 6, output current is from 18.7mA to 1.16mA by adjusting the PWM duty cycle from 5% to 95%. C1 1uF b. Using a DC Voltage Using a variable DC voltage to adjust the brightness is a popular method in some applications. The dimming control using a DC voltage circuit is shown in Figure 5. According to the Superposition Theorem, as the DC voltage increases, the voltage contributed to VFB increases and the voltage drop on R2 decreases, i.e. the LED current decreases. For example, if the VDC range is from 0V to 2.8V, the selection of resistors in Figure 5 sets dimming control of LED current from 20mA to 0mA. D1 OVP SS0520 15V L1 4.7uH to 22uH C2 1uF/16V RT9284A 6 1 LX VDD + VIN 2.7V to 5.5V 4 2 EN GND OVP ILED 5 R2 10k FB 3 R3 13k RDC 3k R1 110 CDC 1uF 2.8V 0V PWM Signal Figure 6. Filtered PWM Signal for LED Dimming Control of RT9284A www.richtek.com 10 DS9284A/B_E-02 August 2006 RT9284A/B Layout Guide ` A full GND plane without gap break. ` VCC to GND noise bypass–Short and wide connection for the 1μF MLCC capacitor between Pin6 and Pin2. ` Minimized LX node copper area to reduce EMI. ` Minimized FB node copper area and keep far away from noise sources. 20 18 LED Current (mA) 16 14 12 10 8 6 4 2 0 0 10 20 30 40 50 60 70 80 90 100 PWM Duty (%) Figure 7 Inductor Selection The recommended value of inductor for 3 to 5 WLEDs applications are 4.7 to 22μH. Small size and better efficiency are the major concerns for portable device, such as RT9284A/B used for mobile phone. The inductor should have low core loss at 1.2MHz and low DCR for better efficiency. To avoid inductor saturation current rating should be considered. Figure 8. Top Layer Capacitor Selection Input and output ceramic capacitors of 1μF are recommended for RT9284A/B applications. For better voltage filtering, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of their wider voltage and temperature ranges. Diode Selection Schottky diode is a good choice for RT9284A/B because of its low forward voltage drop and fast reverse recovery. Using Schottky diode can get better efficiency. The highspeed rectification is also a good characteristic of Schottky diode for high switching frequency. Current rating of the diode must meet the root mean square of the peak current and output average current multiplication as following : Figure 9. Bottom Layer ID (RMS) ≈ (IOUT × IPEAK ) The diode’ s reverse breakdown voltage should be larger than the output voltage. SS0520 is recommended Schottky diode for rectifier. DS9284A/B_E-02 August 2006 www.richtek.com 11 RT9284A/B Outline Dimension H D L B C b A A1 e Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 1.000 0.028 0.039 A1 0.000 0.100 0.000 0.004 B 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 C 2.591 3.000 0.102 0.118 D 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 H 0.080 0.254 0.003 0.010 L 0.300 0.610 0.012 0.024 TSOT-23-5 Surface Mount Package www.richtek.com 12 DS9284A/B_E-02 August 2006 RT9284A/B H D L C B b A A1 e Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 1.000 0.028 0.039 A1 0.000 0.100 0.000 0.004 B 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 C 2.591 3.000 0.102 0.118 D 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 H 0.080 0.254 0.003 0.010 L 0.300 0.610 0.012 0.024 TSOT-23-6 Surface Mount Package DS9284A/B_E-02 August 2006 www.richtek.com 13