RT mA 3-Channel Pulse Dimming Current Source LED Driver. General Description. Features. Applications. Ordering Information. Pin Configurations

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1 0mA -Channel Pulse Dimming Current Source LED Driver General Description The RT902 is a high performance constant current driver for white LED. It supports up to white LEDs and regulates a constant current for uniform intensity. Each channel supports up to 20mA output current with % typical current accuracy and 0.% typical current matching. The RT902 provides a -step brightness dimming control. The LED current can be easily configured from.25ma to 20mA. The dimming of white LEDs' current can be achieved by applying a pulse signal to the pin. The LED current can be turned off by pin with pull low for 20μs or longer. The typical leakage current is μa while shutdown condition. RT902 is available in a TSOT-2- package (.0mm maximum height). Ordering Information RT902 Package Type J : TSOT-2- Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) 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. Features Support Up to White LEDs Output Current up to 20mA Each Channel Support Pulse and PWM Dimming 0mV Typical Current Source Dropout % Typical LED Current Accuracy 0.% Typical LED Current Matching -Step Brightness Control Low Noise and EMI Low Shutdown Current μa Typical RoHS Compliant and 00% Lead (Pb)-Free Applications Mobile Phone, DSC, MP White LED Backlighting LCD Display Supply Pin Configurations (TOP VIEW) LED2 LED NC LED 2 NC 5 VIN TSOT-2- Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area.

2 Typical Application Circuit V IN 2. to 5.5V C IN.uF VIN RT902 LED LED2 LED Figure. For -WLEDs Application Circuit V IN 2. to 5.5V VIN C IN.uF RT902 LED LED2 LED Figure 2. For 2-WLEDs Application Circuit 0.5us < t HI 0.5us < t LO < 0us 20us < t SHDN % 5/ / / 2/ / 00% 5/ Shutdown x 2/ / Shutdown Figure. Brightness control by pulse dimming. RT902 implements steps brightness control 2

3 Functional Pin Description Pin Number Pin Name Pin Function LED Current Sink for LED. (If not in use, this pin must be connected to VIN) 2, 5 NC No Internal Connection. Power Ground. VIN Input Voltage. Chip Enable. LED Current Sink for LED. (If not in use, this pin must be connected to VIN) LED2 Current Sink for LED2. (If not in use, this pin must be connected to VIN) Function Block Diagram steps Pulse Dimming Controller MHz Oscillator Shut Down Delay Low Dropout Current Source UVLO VIN LED LED2 LED

4 Absolute Maximum Ratings (Note ) Supply Input Voltage V to V Other I/O Pin Voltages V to V VIN, to V Power Dissipation, P T A = 25 C TSOT W Package Thermal Resistance (Note 2) TSOT-2-, θ JA C/W Lead Temperature (Soldering, 0 sec.) C Junction Temperature C Storage Temperature Range C to 50 C ESD Susceptibility (Note ) HBM (Human Body Mode) kV MM (Machine Mode) V Recommended Operating Conditions (Note ) Junction Temperature Range C to 25 C Ambient Temperature Range C to 5 C Electrical Characteristics (V IN =.V, C IN = uf, ESR = 0.0Ω, V F =.V, = 2 = = 20mA, T A = 25 C, unless otherwise specified) Input Parameter Symbol Test Conditions Min Typ Max Unit Input Supply Voltage V IN V Under Voltage Lockout Threshold V IN falling V Under Voltage Lockout Hysteresis mv Shutdown Current I SHDN V = 0V -- 0 μa Quiescent Current I Q V = High, I OUT = ma Output Output Current 00% setting, V LED = V ma Current Matching -LED 00% setting, V LED = V % Dropout Voltage V LED 90% of full output current mv Enable Logic-High V IH Threshold Voltage Logic-Low VIL Time of Logic Logic-High T HI Logic-Low T LO Duration of Logic High for pulse dimming Duration of Logic Low for pulse dimming Shutdown Delay T SHDN From Low to Shutdown 0 20 μs Input Current I V =.V μa V μs

5 Note. 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. θ JA is measured in the natural convection at T A = 25 C on a low effective thermal conductivity test board of JEDEC 5- thermal measurement standard. Note. Devices are ESD sensitive. Handling precaution recommended. Note. The device is not guaranteed to function outside its operating conditions. 5

6 Typical Operating Characteristics 9 Shutdown Current vs. Input Voltage 0. Quiescent Current vs. Input Voltage Shutdown Current (ua) C -0 C 5 C Quiescent Current (ma) C -0 C 5 C Input Voltage (V) Input Voltage (V) LED Current vs. Temperature LED Current vs. Input Voltage LED VF =.2V LED2 VF =.22V 2 20 LED Current (ma) LED Current (ma) LED VF =.V Temperature ( C) Input Voltage (V) Dimming Operation Dimming Operation (5V/Div) (2V/Div) (5mA/Div) VIN =.V (5mA/Div) VIN =.V Time (25μs/Div) Time (00μs/Div)

7 Dimming Operation Turn-On (2V/Div) (2V/Div) I IN (50mA/Div) (5mA/Div) VIN =.V (0mA/Div) VIN =.V Time (0μs/Div) Time (5μs/Div) Turn-Off (2V/Div) IIN (50mA/Div) (0mA/Div) VIN =.V Time (5μs/Div)

8 Application Information Input UVLO The input operating voltage range of the RT902 is 2.V to 5.5V. An input capacitor at the VIN pin could reduce ripple voltage. It is recommended to use a ceramic μf or larger capacitance as the input capacitor. This IC provides an under voltage lockout (UVLO) function to prevent it from unstable issue when startup. The UVLO threshold of input falling voltage is set at 2V typically with a hysteresis 0.2V. Output Current RT902 provides a constant output current for white LED. Figure shows a typical application circuit for white LEDs. Each channel supports up to 20mA output current and regulates a constant current for uniform intensity. For two or one LED application, the non-used channel must be connected to V IN as shown in Figure 2. Brightness Dimming Control The RT902 provides a -step brightness dimming control. The LED current can be easily configured from.25ma to 20mA. The dimming of white LEDs' current can be achieved by applying a pulse signal to the pin. Figure shows the configuration of the -step pulse dimming control operation. The output current is set at 00% of 20mA typical output current when pin pull high initially from shutdown condition. The step change of pulse dimming can be implemented by pin changing with a logic Low pulse. Each step change / of full output current setting. The output current change of pulse dimming is designed in decreasing sequence in terms of (/, 5/,..., /) and then (/, 5/,...) cycle by cycle. The duration of logic Low pulse is between 0.5us and 0μs. The duration of logic High pulse should be longer than 0.5μs. the IC as possible. A short connection is highly recommended. The following guidelines should be strictly followed when designing a PCB layout for the RT902.. All the traces of LED and V IN running from chip to LEDs should be wide and short to reduce the parasitic connection resistance. 2. Input capacitor (C IN ) should be placed close to VIN and connected to ground plane. The anodes of LEDs must be connected to C IN, not battery directly.. The should be connected to a strong ground plane for heat sinking and noise protection. Input capacitor (C IN ) should be placed close to V IN and connected to ground plane. The Anodes of LEDs must connect to C IN, not battery directly. Battery C IN All the traces of LED and V IN running from chip to LEDs should be wide and short to reduce the parasitic connection resistance. LED NC VIN 2 5 LED2 LED NC Ground Plane The should be connected to a strong ground plane for heat sinking and noise protection. Figure. PCB Layout Guide GPIO The LED current can be turned off by pin with pulling low for 20μs or longer. The typical leakage current is μa while shutdown condition. Layout Consideration For best performance, careful PCB layout is necessary. All peripheral components should be placed as close to

9 Outline Dimension D H L C B b A e A Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A A B b C D e H L TSOT-2- Surface Mount Package Richtek Technology Corporation Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: ()5529 Fax: ()552 Richtek Technology Corporation Taipei Office (Marketing) 5F, No. 95, Minchiuan Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (2)299 Fax: (2)2 marketing@richtek.com 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. 9