RT9285APQW

Preliminary RT9285A/B Tiny Package, High Performance, Diode Embedded White LED Driver General Description The RT9285 is a high frequency asynchronous boost converter with internal diode, which can support 2 to 5 White LEDs for backlighting and OLED power supply. The Internal soft start function can reduce the inrush current. The device operates with 1MHz fixed switching frequency to allow small external components and to simplify possible EMI problems. The device comes with 20V over voltage protection to allow inexpensive and small-output capacitors with lower voltage rating. The LED current is initially set with the external sense resistor RSET , and the feedback voltage is 250 mV. Tiny package type TSOT-23-6 and WDFN-8L 2x2 packages provide the best solution for PCB space saving and total BOM cost. Features l l l l l l l l l l l VIN Operating Range : 2.7V to 5.5V Up to 85% Efficiency 22V Internal Power N-MOSFET 1MHz Switching Frequency Built-in Diode Digital Dimming with Zero-Inrush Input UVLO Protection Output Over Voltage Protection Internal Soft Start and Compensation TSOT-23-6 and 8-Lead WDFN Package RoHS Compliant and 100% Lead (Pb)-Free Applications l l l Ordering Information RT9285 Package Type QW : WDFN-8L 2x2 (W-Type) J6 : TSOT-23-6 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) Dimming A : Digital Pulse Dimming B : PWM Clock Dimming Note : Richtek Pb-free and Green products are : l l l Cellular Phones Digital Cameras PDAs and Smart Phones Porbable Instruments MP3 Player OLED Power Pin Configurations (TOP VIEW) VDD VOUT EN AGND LX NC PGND 1 2 3 4 8 }RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. 9 7 6 5 FB EN VOUT VDD 6 1 LX 5 2 GND 4 3 FB }Suitable for use in SnPb or Pb-free soldering processes. }100%matte tin (Sn) plating. WDFN-8L 2x2 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. 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. DS9285A/B-02 August 2007 www.richtek.com 1 RT9285A/B Typical Application Circuit Preliminary L1 10uH to 22uH VIN 2.7V to 5.5V RT9285A/B LX EN Chip Enable GND FB VDD VOUT C1 1uF C2 0.22uF to 1uF RSET 12.5 Functional Pin Description Pin No. Pin Name W DFN-8L 1 2 -3, Exposed Pad (9) 4 5 TSOT-23-6 -1 2 --6 AGND LX GND NC PGND VDD Analog Ground Pin. LX Pin. Connect this Pin to an inductor. Minimize the track area to reduce EMI. Ground Pin. No Internal Connection. Power Ground Pin. Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input ripple. Output Voltage pin. The pin internally connects to OVP diode to limit output voltage while LEDs are disconnected. Chip Enable (Active High). Note that this pin has an internal pull- down resistance around 300k Ω. Feedback Pin. Series connecting a resistor between WLED and 8 3 FB ground as a current sense. Sense the current feedback voltage to set the current rating. -GND Exposed pad should be soldered to PCB board and connected to GND. Pin Function 6 5 VOUT 7 4 EN www.richtek.com 2 DS9285A/B-02 August 2007 Preliminary Function Block Diagram Current Sense RT9285A/B 1.0MHz OSC Slope Compensation OCP OVP PWM Logic LX VOUT VDD UVLO/P GOOD + Timer Dimming Controller + Soft Start/Cla mping EN FB VREF GND Operation Soft-Start The Soft-Start function is made by clamping the output voltage of error amplifier with another voltage source that is increased slowly from zero to near VIN in the Soft-Start period. Therefore, the duty cycle of the PWM will be increased from zero to maximum in this period. The softstart time is decided by a timer of 1.5ms. The charging time of the inductor will be limited as the smaller duty so that the inrush current can be reduced to an acceptable value. Over Voltage Protection The Over Voltage Protection is detected by a junction breakdown detecting circuit. Once VOUT goes over the detecting voltage, LX pin stops switching and the power NMOS is turned off. Then, the VOUT is clamped to be near VOVP. LED Current Setting The RT9285 regulates the LED current by setting the current sense resistor (RSET ) connecting to feedback and ground. The internal feedback reference voltage is 0.25V. The LED current can be set from following equation easily. ILED (mA) = 0.25/RSET In order to have an accurate LED current, precision resistors are preferred (1% is recommended). The table for RSET selection is shown below. Table 1. RSET Value Selection ILED (mA) 5 10 12 15 20 RSET (Ω) 49.9 24.9 21 16.5 12.4 Digital Pulse Dimming (RT9285A) The digital pulse dimming is implemented by checking the low-level duration time of EN pin. As the duration time is in the range of TUP, the LED current will increase 1/16. If the duration time is in the range of TDOWN, the LED current will decrease 1/16. The high-level duration time of EN pin needs larger than TDELAY to make sure the logic can be detected correctly. As the LED current is set to MAX (16/ 16), it will keep MAX until the decreasing signal is detected. On the other hand, as the LED current is set to MIN (1/16), it will keep MIN until the increasing signal is detected. When the chip turns on, the initial state of LED current is MAX. DS9285A/B-02 August 2007 www.richtek.com 3 RT9285A/B Preliminary Table 2 Feedback Voltage Increase Decrease Delay between steps Shutdown Time 0.5µs to 75µs 180µs to 300µs > 0.5µs > 1ms Symbol TUP TDOWN TDELAY TSHDN TDELAY EN TDOWM Shut-down IWLED 100% TUP 15/16 100% TSHDN Shut-down Figure 1 PWM Dimming (RT9285B) For controlling the LED brightness, the RT9285B can perform the dimming control by applying a PWM signal to EN pin. A low pass filter is implemented inside chip to reduce the slew rate of ILED to prevent the audio noise. 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. EN IWLED, AVG = Duty of EN IWLED Figure 2 Current Limiting The current flow through the inductor as charging period is detected by a current sensing circuit. As the value over the current limiting, the NMOS will be turned-off so that the inductor will be forced to leave charging stage and enter discharging stage. Therefore, the inductor current will not increase over the current limiting. www.richtek.com 4 DS9285A/B-02 August 2007 Preliminary Absolute Maximum Ratings l RT9285A/B (Note 1) Supply Voltage, VIN ------------------------------------------------------------------------------------------------- −0.3 to 6V l LX Input Voltage ------------------------------------------------------------------------------------------------------ − 0.3V to 22V l Output Voltage ------------------------------------------------------------------------------------------------------- − 0.3V to 21V l The other pins -------------------------------------------------------------------------------------------------------- − 0.3V to 6V l Power Dissipation, PD @ TA = 25°C TSOT23-6 -------------------------------------------------------------------------------------------------------------- 0.455W WDFN-8L 2x2 --------------------------------------------------------------------------------------------------------- 0.606W l Package Thermal Resistance (Note 4) TSOT23-6, θJA -------------------------------------------------------------------------------------------------------- 220°C/W WDFN-8L 2x2, θJA --------------------------------------------------------------------------------------------------- 165°C/W l Junction Temperature ----------------------------------------------------------------------------------------------- 150°C l Lead Temperature (Soldering, 10 sec.)-------------------------------------------------------------------------- 260°C l Storage Temperature Range --------------------------------------------------------------------------------------- − 65°C to 150°C l ESD Susceptibility (Note 2) HBM (Human Body Mode) ----------------------------------------------------------------------------------------- 2kV MM (Machine Mode) ------------------------------------------------------------------------------------------------ 200V Recommended Operating Conditions l l (Note 3) Operation Junction Temperature Range ------------------------------------------------------------------------- −40°C to 125°C Operation Ambient Temperature Range ------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 3.7V, FREQ left floating, TA = 25° C, unless otherwise specification) Parameter System Supply Input Operation voltage Range Under Voltage Lock Out Quiescent Current Supply Current Shut Down Current Output Line Regulation Oscillator Operation Frequency Maximum Duty Cycle Reference Voltage Feedback Reference Voltage Diode Forward Voltage MOSFET On Resistance of MOSFET Symbol V IN V UVLO IQ I IN I SHDN Test Condition Min 2.7 1.7 Typ -2 300 -2 -1 90 0.25 0.9 0.75 Max 5.5 2.3 450 2 5 3 --0.263 -1 Units V V µA mA uA % MHz % V V Ω FB = 1.5V, No switch FB = 0V, Switch VEN < 0.4V V IN = 3V to 4.3V -----85 f OSC VREF VFW R DS(ON) IFW = 100mA 0.237 -0.5 To be continued DS9285A/B-02 August 2007 www.richtek.com 5 RT9285A/B Parameter Protection OVP Threshold OCP Control Interface EN Threshold Logic-Low Voltage VIL VOVP Symbol Preliminary Test Condition Min Typ Max Units --- 20 400 --- V mA -1.4 --- 0.4 -- V V Logic-High Voltage VIH Digital Dimming (for RT9285A) Up Brightness Time Down Brightness Time Delay Between Steps Time Shut Down Delay Time TUP TDOWN TDELAY TSHDN Refer to Figure 1 Refer to Figure 1 Refer to Figure 1 Refer to Figure 1 0.5 180 0.5 1 ----- 75 300 --- µs µs µs ms 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. D evices are ESD sensitive. Handling precaution recommended. Note 3. T he device is not guaranteed to function outside its operating conditions. Note 4. θJA is measured in the natural convection at T A = 2 5 ° C on a low effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard. www.richtek.com 6 DS9285A/B-02 August 2007 Preliminary Typical Operating Characteristics OVP vs. Input Voltage 20.8 20.4 20 RT9285A/B Efficiency vs. Input Voltage 90 90% 4W-LED 85 85% 80 80% Efficienc y (% ) 2.6 3 3.4 3.8 4.2 4.6 5 5.4 5.8 6.2 O VP (V) 75 75% 70% 70 65% 65 60% 60 55% 55 50% 50 2.5 3 3.5 4 4.5 5 5.5 6 19.6 19.2 18.8 18.4 18 Input Voltage (V) Input Voltage (V) Quiescent Current vs. Input Voltage 450 400 1.02 1.00 Frequency vs. Input Voltage Quie sce nt Current (uA) -40°C F requ enc y (M Hz) 350 300 250 200 150 100 25°C 85°C 0.98 0.96 0.94 0.92 0.90 0.88 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 2.6 3.1 3.6 4.1 4.6 5.1 5.6 Input Voltage (V) Input Voltage (V) Enable Voltage vs. Input Voltage 0.84 0.83 0.82 17 16 Output Voltage vs. Output Current Enable Voltage En able Voltage (V) Ou tpu t Voltage (V) 0.81 0.80 0.79 0.78 0.77 0.76 0.75 0.74 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 15 14 13 12 11 10 5 15 25 35 45 55 65 75 Shutdown Voltage Input Voltage (V) Output Current (mA) DS9285A/B-02 August 2007 www.richtek.com 7 RT9285A/B Preliminary Feedback Reference Voltage vs. Input Voltage 253.5 Dimming Operation @ Decreace VIN (2V/Div) VOUT (5V/Div) VIN = 3.7V Fe edb ack Re fere nce Voltage (mV) 253.0 252.5 252.0 251.5 251.0 250.5 250.0 249.5 249.0 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5 EN (2V/Div) ILED (10mA/Div) Time (500 µs/Div) Input Voltage (V) Dimming Operation @ Increase VIN (2V/Div) VOUT (5V/Div) VIN = 3.7V Inrush Current Response VIN (2V/Div) VIN = 3.7V VOUT (5V/Div) EN (2V/Div) ILED (10mA/Div) Time (500 µs/Div) EN (2V/Div) IIN (100mA/Div) Time (500 µs/Div) www.richtek.com 8 DS9285A/B-02 August 2007 Preliminary Application Information LED Current Control The RT9285A/B regulates the LED current by setting the current sense resistor (RSET ) connecting to feedback and ground. The RT9284A/B feedback voltage (VFB) is 0.25V. The LED current (ILED) can be set by a resistor RSET . ILED = 0.25/RSET In order to have an accurate LED current, a precision resistor is preferred (1% is recommended). L1 10uH to 22uH VIN 2.7V to 5.5V RT9285A/B The inductor saturation current rating should be considered to cover the inductor peak current. Capacitor Selection Input and output ceramic capacitors of 1µF are recommended for RT9285A/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. Output Voltage Control The output voltage of R9285 can be adjusted by the divider circuit on FB pin. Figure 6 shows a 2-level voltage control circuit for OLED application. The output voltage can be calculated by the following equations in Figure 6. L1 10uH to 22uH VIN 2.7V to 5.5V RT9285A/B LX EN Chip Enable GND FB VDD VOUT C1 1uF C2 0.22uF to 1uF RSET 12.5 RT9285A/B C1 1uF VOUT 15V Figure 3. Application for Driving 4 Series WLEDs VIN 2.7V to 5.5V LX EN Chip Enable GND VDD VOUT C2 0.22uF to 1uF FB R2 10k R1 590k L1 10uH to 22uH RT9285A/B LX EN Chip Enable GND FB VDD VOUT C1 1uF VOUT = 0.25 × R1 + R2 ; R2 > 10k R2 Figure 5. Application for Constant Output Voltage C2 0.22uF to 1uF VIN RSET 12.5 GPIO RT9285A/B VDD VOUT RA R GPIO RB EN GND OLED Figure 4. Application for Driving 5 Series WLEDs Inductor Selection The recommended value of inductor for 4 to 5WLEDs applications are 10µH to 22 µH. For 3W LEDs, the recommended value of inductor is 4.7µH to 22µH. Small size and better efficiency are the major concerns for portable device, such as RT9285A/B used for mobile phone. The inductor should have low core loss at 1MHz and low DCR for better efficiency. DS9285A/B-02 August 2007 VEN LX FB Figure 6. Application Circuit for Output Voltage Control and Related Equations www.richtek.com 9 RT9285A/B VOUT = RA x {(FB/RB) + (FB-GPIO)/RGPIO} + FB As GPIO = 0V, VOUT = RA x {(0.25/RB) + (0.25/RGPIO)} + 0.25 As GPIO = 2.8V, Preliminary (1) } LX node copper area should be minimized for reducing EMI. (*1) } The input capacitor C1 should be placed as closed as possible to Pin 6. (*2) } The output capacitor C2 should be connected directly from the Pin 5 to ground rather than across the LEDs. (*3) } FB node copper area should be minimized and keep far away from noise sources (Pin 1, Pin 5, Pin 6). (*4) } The Inductor is far away receiver and microphone. } The voice trace is far away RT9285. } The embedded antenna is far away and different side RT9285. } R1 should be placed as close as RT9285. } The through hole of RT9285's GND pin is recommended as large and many as possible. (2) VOUT = RA x {(0.25/RB) + (0.25-2.8)/RGPIO )} + 0.25 (3) As GPIO = 1.8V, VOUT = RA x {(0.25/RB) + (0.25-1.8)/ RGPIO)} + 0.25 (4) For Efficiency Consideration : Set RA = 990kΩ, If 2 levels are 16V (GPIO = 0V) and 14V (GPIO = 1.8V) Get RB = 16kΩ, RGPIO = 890kΩ Table 3. Suggested Resistance for Output Voltage Control RA RB RGPIO Conditions ( kΩ ) (k Ω ) (k Ω ) Case A : Normal Voltage = 16V (GPIO = 0V) Dimming Voltage = 12V (GPIO = 1.8V) Case B : Normal Voltage = 16V (GPIO = 0V) Dimming Voltage = 12V (GPIO = 2.8V) 1200 19.5 840 1100 18 495 L1 VIN C1 *1 LX GND GND RSET *4 FB 3 4 EN EN 1 2 6 5 *2 VDD VOUT C2 *3 WLEDs Figure 7. TOP Considering the output voltage deviation from the GPIO voltage tolerance, as GPIO voltage vibrated by 0 ± 50mV and 1.8(2.8) ±5% ,the output voltage could be kept within ±2.5%. Layout guide } A full GND plane without gap break. } Traces in bold need to be routed first and should be kept as short as possible. } VDD to GND noise bypass : Short and wide connection for the 1uF MLCC capacitor between Pin 6 and Pin 2. www.richtek.com 10 DS9285A/B-02 August 2007 Figure 8. Bottom Preliminary Outline Dimension RT9285A/B H D L C B b A A1 e Symbol A A1 B b C D e H L Dimensions In Millimeters Min 0.700 0.000 1.397 0.300 2.591 2.692 0.838 0.080 0.300 Max 1.000 0.100 1.803 0.559 3.000 3.099 1.041 0.254 0.610 Dimensions In Inches Min 0.028 0.000 0.055 0.012 0.102 0.106 0.033 0.003 0.012 Max 0.039 0.004 0.071 0.022 0.118 0.122 0.041 0.010 0.024 TSOT-23-6 Surface Mount Package DS9285A/B-02 August 2007 www.richtek.com 11 RT9285A/B Preliminary D D2 L E E2 SEE DETAIL A 1 e A A1 A3 b 2 1 2 1 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. Symbol A A1 A3 b D D2 E E2 e L Dimensions In Millimeters Min 0.700 0.000 0.175 0.200 1.950 1.000 1.950 0.400 0.500 0.300 0.400 Max 0.800 0.050 0.250 0.300 2.050 1.250 2.050 0.650 D imensions In Inches Min 0.028 0.000 0.007 0.008 0.077 0.039 0.077 0.016 0.020 0.012 0.016 Max 0.031 0.002 0.010 0.012 0.081 0.049 0.081 0.026 W-Type 8L DFN 2x2 Package Richtek Technology Corporation Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Richtek Technology Corporation Taipei Office (Marketing) 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com www.richtek.com 12 DS9285A/B-02 August 2007