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. Ordering Information RT9284 (- z z z z z z z z z Applications z ) Package Type J5 : TSOT-23-5 J6 : TSOT-23-6 Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) OVP Voltage 15 : 15V 20 : 20V FB Voltage A : 1.235V B : 0.25V VIN Operating Range : 2.7V to 5.5V Maximum Output Voltage up to 20V Dimming with Zero-inrush and Wide Frequency Range of 100 to 100kHz 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 z z z z Camera Flash White LED Mobile Phone, Smart Phone LED Backlight PDA LED Backlight Digital Still Camera Camcorder Pin Configurations TOP VIEW VDD EN 5 4 2 3 Note : LX GND FB Richtek products are : TSOT-23-5 ` 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. DS9284A/B-07 April 2011 VDD OVP EN 6 5 4 2 3 LX GND FB TSOT-23-6 www.richtek.com 1 RT9284A/B Typical Application Circuit D1 SS0520 L1 4.7uH to 22uH VIN + 2.7V to 5.5V C1 1uF 6 4 Dimming Control 100Hz-100kHz 2 OVP 15V RT9284 1 LX VDD EN OVP ILED C2 1uF/16V 5 FB 3 GND R1 Figure 1. Application for Driving 3 Series WLEDs D1 SS0520 L1 4.7uH to 22uH VIN + 2.7V to 5.5V C1 1uF 6 4 Dimming Control 100Hz-100kHz 2 R2 600k RT9284 1 VDD LX EN OVP OVP 18V C2 1uF/25V ILED 5 OVP 15V FB 3 GND R1 Figure 2. Application for Driving 4 Series WLEDs D1 SS0520 L1 4.7uH to 22uH VIN + 2.7V to 5.5V C1 1uF 6 Dimming Control 100Hz-100kHz 4 2 OVP 20V C2 1uF/25V RT9284B 1 VDD LX EN GND OVP ILED 5 FB 3 VFB = 0.25V 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 6 4 2 RT9284A 1 LX VDD EN GND OVP VOUT 12V R1 130k C2 1uF/16V 5 FB 3 VFB = 1.235V R2 15k Figure 4. Application for Constant Output Voltage www.richtek.com 2 DS9284A/B-07 April 2011 RT9284A/B Pin Description Pin No. Pin Name Pin Function TSOT-23-5 TSOT-23-6 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 4 4 EN -- 5 OVP 5 6 VDD 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. 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. Over Voltage Protection Pin. Voltage sensing input to trigger the function of over voltage protection. Leave it unconnected to disable this function. 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-07 April 2011 Timer 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 ---------------------------------------------------------------------------------------------------LX Input Voltage ---------------------------------------------------------------------------------------------------------OVP Voltage -------------------------------------------------------------------------------------------------------------The Other Pins ----------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C TSOT-23-5 ----------------------------------------------------------------------------------------------------------------TSOT-23-6 ----------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) TSOT-23-5, θJA -----------------------------------------------------------------------------------------------------------TSOT-23-6, θJA -----------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------------Junction Temperature --------------------------------------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Mode) --------------------------------------------------------------------------------------------MM (Machine Mode) ---------------------------------------------------------------------------------------------------- Recommended Operating Conditions z z z −0.3V to 7V −0.3V to 22V −0.3V to 22V −0.3V to 6V 0.455W 0.455W 220°C/W 220°C/W 260°C 150°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage ---------------------------------------------------------------------------------------------------- 2.7V to 5.5V 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 Conditions Min Typ Max Unit System Supply Input Operation voltage Range V DD 2.7 -- 5.5 V Under Voltage Lock Out V DD 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 V EN < 0.4V -- -- 1 uA V IN : 3.0~4.3V -- 3 -- % 0.9 1.2 1.5 MHz Maximum Duty Cycle 85 -- -- % Dimming Frequency 100 -- 100k Hz RT9284A 1.173 1.235 1.296 RT9284B 0.237 0.25 0.263 Line Regulation Oscillator Operation Frequency fOSC Reference Voltage Feedback Voltage (Note 5) V To be continued www.richtek.com 4 DS9284A/B-07 April 2011 RT9284A/B Parameter Symbol Test Condition Min Typ Max Unit -- 0.75 -- Ω for 2,3,4 WLEDs application 14 15 16 for 5 WLED application 19 20 21 OVP Sink Current -- 5 -- μA OCP -- 750 -- mA MOSFET On Resistance of MOSFET RDS(ON) Protection OVP Threshold V OVP V Shut Down Voltage V EN -- -- 0.4 V Enable Voltage V EN 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. θJA is measured in the natural convection at TA = 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 recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. Floating the OVP pin to disable OVP function. DS9284A/B-07 April 2011 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-07 April 2011 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 1 0 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 (10mA/Div) ILED f = 1kHz, Duty = 50% Time (400μs/Div) DS9284A/B-07 April 2011 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) ILED 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-07 April 2011 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-07 April 2011 Time (400ns/Div) www.richtek.com 9 RT9284A/B Application Information Power Sequence b. Using a DC Voltage The RT9284A/B must take notice of the power sequence. The power sequence of RT9284A/B has to VDD early than EN or else the RT9284A/B maybe fall into the unknown state to result in RT9284A/B turn off. Using a variable DC voltage to adjust the brightness is a V DD > 2.7V V DD EN > 1.5V EN EN < 0.4V popular method in some applications. The dimming control using a DC voltage circuit is shown in Figure 6. 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 6 sets dimming control of LED current from 20mA to 0mA. V OUT V IN 2.7V to 5.5V C1 D1 SS0520 L1 4.7uH to 22uH Figure 5 LED Current Control 6 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). 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 RT9284A V EN > 1.5V VEN < 0.4V 4 2 VDD EN GND LX OVP 1 5 R2 10k FB 3 R3 13k R1 110 V DC Dimming 0V to 2.8V Figure 6. Dimming Control Using a DC Voltage for RT9284A The LED current can be calculated by the following equation. VFB − ILED = R2 × (VDC − VFB ) R3 R1 c. Using a Filtered PWM signal: 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 from100 to100kHz 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. www.richtek.com 10 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 7. 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. Figure 8. shows the relationship between LED current and PWM duty cycle. DS9284A/B-07 April 2011 RT9284A/B V IN 2.7V to 5.5V D1 SS0520 L1 4.7uH to 22uH C1 Capacitor Selection ILED C2 RT9284A 6 1 VDD LX V EN > 1.5V V EN < 0.4V 4 2 EN OVP 5 R2 10k FB 3 GND R3 10k R DC 3k R1 110 Figure 7. Filtered PWM Signal for LED Dimming Control of RT9284A The LED current can be calculated by the following equation. ILED = Diode Selection Schottky diode is a good choice for RT9284A/B because of its low forward voltage drop and fast reverse recovery. C DC 1uF 2.8V 0V PWM Signal VFB − 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. 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 : ID (RMS) ≈ (IOUT × IPEAK ) R2 × (VPWM × Duty − VFB ) R3 + RDC R1 The diode’ s reverse breakdown voltage should be larger than the output voltage. SS0520 is recommended Schottky diode for rectifier. 20 18 Layout Guide z A full GND plane without gap break. z VCC to GND noise bypass–Short and wide connection for the 1μF MLCC capacitor between Pin6 and Pin2. z Minimized LX node copper area to reduce EMI. z Minimized FB node copper area and keep far away from noise sources. 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 8 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. DS9284A/B-07 April 2011 Figure 9. Top Layer www.richtek.com 11 RT9284A/B Figure 10. Bottom Layer www.richtek.com 12 DS9284A/B-07 April 2011 RT9284A/B Outline Dimension H D L B C b A A1 e Dimensions In Millimeters Dimensions In Inches Symbol 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 DS9284A/B-07 April 2011 www.richtek.com 13 RT9284A/B H D L C B b A A1 e Dimensions In Millimeters Dimensions In Inches Symbol 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 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. www.richtek.com 14 DS9284A/B-07 April 2011