RT9285CGQW

RT9285C Tiny Package, High Performance, Diode Embedded White LED Driver General Description Features The RT9285C 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 250mV. Tiny package type TSOT-23-6, XDFN-8L 2x2 and WDFN-8L 2x2 packages provide the best solution for PCB space saving and total BOM cost. z z z z z z z z z z z Applications z Ordering Information z RT9285C z Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) Z : ECO (Ecological Element with Halogen Free and Pb free) Note : Richtek products are : ` RoHS compliant and compatible with the current require- z z z Cellular Phones Digital Cameras PDAs and Smart Phones Porbable Instruments MP3 Player OLED Power Pin Configurations (TOP VIEW) GND LX NC PGND 1 2 3 FB EN VOUT VDD 8 GND Package Type QW : WDFN-8L 2x2 (W-Type) QX : XDFN-8L 2x2 (X-Type) J6 : TSOT-23-6 VIN Operating Range : 2.7V to 5.5V Up to 85% Efficiency 22V Internal Power NMOS 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, 8-Lead XDFN and WDFN Package RoHS Compliant and 100% Lead (Pb)-Free 9 4 7 6 5 XDFN/WDFN-8L 2x2 ments of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. VDD VOUT EN 6 Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area. DS9285C-03 March 2011 LX 5 4 2 3 GND FB TSOT-23-6 www.richtek.com 1 RT9285C Typical Application Circuit VIN 2.7V to 5.5V L1 10µH to 22µH C1 1µF RT9285C VDD LX VOUT EN C2 0.22µF to 1µF Chip Enable GND FB RSET 12.5 PGND PGND pin for XDFN/WDFN-8L Packages Function Pin Description Pin No. XDFN/WDFN-8L TSOT-23-6 1, Pin Name Pin Function Ground Pin. The exposed pad must be soldered to a large PCB and 2 GND 2 1 LX 3 -- NC No Internal Connection. 4 -- PGND Power Ground Pin. 5 6 VDD 6 5 VOUT 7 4 EN 9 (Exposed Pad) connected to GND for maximum power dissipation. LX Pin. Connect this Pin to an inductor. Minimize the track area to reduce EMI. Supply Input Voltage Pin. Bypass 1μF 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 300kΩ. 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. 0.5µs < tHI EN Shutdown IWLED 0 1 0.5µs < tLO < 300µs 2 3 4 100% 15/16 14/16 13/16 12/16 5 14 15 0 1 100% 3/16 2/16 1/16 15/16 Shutdown Figure 1. Operation of Digital Pulse Dimming Control www.richtek.com 2 DS9285C-03 March 2011 RT9285C Function Block Diagram 1.0MHz OSC Current Sense Slope Compensation OCP LX PWM Logic OVP VOUT UVLO/P GOOD VDD EN FB VREF + Timer Dimming Controller + - Soft Start/ Clamping PGND 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 RT9285C 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 DS9285C-03 March 2011 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) RSET (Ω) 5 49.9 10 24.9 12 21 15 16.5 20 12.4 Digital Pulse Dimming Control RT9285C implements the pulse dimming method being used to control the brightness of white LEDs. There are 16 steps to set the current of white LEDs. The maximum LED current is up to 20mA that is sufficient for most application in backlight. The detail operation of brightness dimming is showed in the Figure 1. 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 3 RT9285C Absolute Maximum Ratings (Note 1) Supply Voltage, VIN --------------------------------------------------------------------------------------------------- −0.3 to 6V LX Input Voltage ------------------------------------------------------------------------------------------------------- − 0.3V to 22V z Output Voltage --------------------------------------------------------------------------------------------------------- − 0.3V to 21V z The other pins ---------------------------------------------------------------------------------------------------------- − 0.3V to 6V z Power Dissipation, PD @ TA = 25°C TSOT23-6 --------------------------------------------------------------------------------------------------------------- 0.392W XDFN/WDFN-8L 2x2 -------------------------------------------------------------------------------------------------- 0.606W z Package Thermal Resistance (Note 2) TSOT23-6, θJA ---------------------------------------------------------------------------------------------------------- 255°C/W XDFN/WDFN-8L 2x2, θJA --------------------------------------------------------------------------------------------- 165°C/W XDFN/WDFN-8L 2x2, θJC -------------------------------------------------------------------------------------------- 20°C/W z Junction Temperature ------------------------------------------------------------------------------------------------- 150°C z Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260°C z Storage Temperature Range ---------------------------------------------------------------------------------------- − 65°C to 150°C z z 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, FREQ left floating, TA = 25°C, Unless Otherwise specification) Parameter Min Typ Max Unit V IN 2.7 -- 5.5 V Under Voltage Lock Out V UVLO 1.7 2 2.3 V Quiescent Current Supply Current IQ IIN FB = 1.5V, No switch FB = 0V, Switch --- 300 -- 450 2 μA mA Shut Down Current ISHDN V EN < 0.4V -- 2 5 μA V IN = 3V to 4.3V -- -- 3 % -- 1 -- MHz 85 90 -- % 0.237 0.25 0.263 V -- 0.9 -- V 0.5 0.75 1 Ω --- 20 400 --- V mA System Supply Input Operation voltage Range Symbol Output Line Regulation Oscillator Operation Frequency Test Conditions fOSC Maximum Duty Cycle Reference Voltage Feedback Reference Voltage Diode V REF Forward Voltage V FW MOSFET On Resistance of MOSFET RDS(ON) Protection OVP Threshold OCP VOVP IFW = 100mA To be continued www.richtek.com 4 DS9285C-03 March 2011 RT9285C Parameter Symbol Test Conditions Min Typ Max -- -- 0.4 1.4 -- -- Unit Control Interface EN Threshold Logic-Low Voltage VIL Logic-High Voltage VIH V EN Low Time for Dimming TLO Refer to Figure 1 0.5 -- 300 μs Delay Between Steps Time THI Refer to Figure 1 0.5 -- -- μs EN Low Time for Shut Down TSHDN Refer to Figure 1 1 -- -- 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. 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 3. The device is not guaranteed to function outside its operating conditions. DS9285C-03 March 2011 www.richtek.com 5 RT9285C Typical Operating Characteristics OVP vs. Input Voltage Efficiency vs. Input Voltage 20.8 90 20.4 85 80 Efficiency (%) 20 OVP (V) 4W-LED 19.6 19.2 18.8 75 70 65 60 18.4 55 18 50 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5 2.8 3.1 3.4 3.7 4.6 4.9 5.2 5.5 5.2 5.5 Frequency vs. Input Voltage Quiescent Current vs. Input Voltage 450 1.02 400 1.00 -40°C 350 Frequency (MHz) Quiescent Current (uA) 4.3 Input Voltage (V) Input Voltage (V) 25°C 300 85°C 250 200 150 0.98 0.96 0.94 0.92 0.90 0.88 100 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 Input Voltage (V) Input Voltage (V) Output Voltage vs. Output Current Enable Voltage vs. Input Voltage 17 0.84 0.83 16 Enable Voltage 0.82 Output Voltage (V) Enable Voltage (V) 4 0.81 0.80 0.79 0.78 Shutdown Voltage 0.77 0.76 15 14 13 12 11 0.75 10 0.74 2.8 3.1 3.4 3.7 4 4.3 4.6 Input Voltage (V) www.richtek.com 6 4.9 5.2 5.5 5 15 25 35 45 55 65 75 Output Current (mA) DS9285C-03 March 2011 RT9285C Feedback Reference Voltage vs. Input Voltage Dimming Operation @ Decreace Feedback Reference Voltage (mV) 253.5 VIN (2V/Div) VOUT (5V/Div) 253.0 252.5 VIN = 3.7V 252.0 251.5 251.0 EN (2V/Div) 250.5 250.0 ILED (10mA/Div) 249.5 249.0 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5 Time (500μs/Div) Input Voltage (V) Inrush Current Response VIN (2V/Div) VIN = 3.7V VOUT (5V/Div) EN (2V/Div) IIN (100mA/Div) Time (500μs/Div) DS9285C-03 March 2011 www.richtek.com 7 RT9285C Application Information LED Current Control Capacitor Selection The RT9285C 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 . Input and output ceramic capacitors of 1µF are recommended for RT9285C 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. ILED = 0.25/RSET In order to have an accurate LED current, a precision resistor is preferred (1% is recommended). L1 10µH to 22µH RT9285C LX VIN 2.7V to 5.5V Output Voltage Control The output voltage of R9285C can be adjusted by the divider circuit on FB pin. Figure 5 shows a 2-level voltage control circuit for OLED application. The output voltage can be calculated by the following equations in Figure 5. C1 1µF L1 10µH to 22µH VDD EN VOUT Chip Enable GND C2 0.22µF to 1µF LX RSET 12.5 Figure 2. Application for Driving 4 Series WLEDs RT9285C LX EN VOUT VDD VOUT EN Chip Enable GND R1 590k C2 0.22µF to 1µF FB R2 10k R1 + R2 VOUT = 0.25 × ; R2 > 10k R2 Figure 4. Application for Constant Output Voltage C1 1µF GPIO VIN VDD Chip Enable GND VIN 2.7V to 5.5V VOUT 15V C1 1µF RT9285C FB L1 10µH to 22µH VIN 2.7V to 5.5V RT9285C VDD C2 0.22µF to 1µF VOUT RA R GPIO FB RSET 12.5 LX FB EN GND OLED RB VEN Figure 3. Application for Driving 5 Series WLEDs Inductor Selection The recommended value of inductor for 4 to 5WLEDs applications are 10µH to 22µH. 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 RT9285C used for mobile phone. The inductor should have low core loss at 1MHz and low DCR for better efficiency. The inductor saturation current rating should be considered to cover the inductor peak current. www.richtek.com 8 Figure 5. Application Circuit for Output Voltage Control and Related Equations VOUT = RA x {(FB/RB) + (FB-GPIO)/RGPIO} + FB (1) As GPIO = 0V, VOUT = RA x {(0.25/RB) + (0.25/RGPIO)} + 0.25 (2) As GPIO = 2.8V, VOUT = RA x {(0.25/RB) + (0.25-2.8)/RGPIO )} + 0.25 (3) DS9285C-03 March 2011 RT9285C 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 2. Suggested Resistance for Output Voltage Control Conditions RA RB RGPIO (kΩ) (kΩ) (kΩ) Case A : Normal Voltage = 16V (GPIO = 0V) 1100 18 495 Dimming Voltage = 12V (GPIO = 1.8V) temperature of the die (125°C) and TA is the maximum ambient temperature. The junction to ambient thermal resistance θJA is layout dependent. For XDFN/WDFN 2x2 packages, the thermal resistance θJA is 165°C/W on the standard JEDEC 51-3 single layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by following formula: PD(MAX) = (125°C − 25°C) / (165°C/W) = 0.606 W for WDFN/ XDFN 2x2 packages PD(MAX) = (125°C − 25°C) / (255°C/W) = 0.392 W for TSOT23-6 packages The maximum power dissipation depends on operating ambient temperature for fixed T J (MAX) and thermal resistance θJA. For RT9285C packages, the Figure 6 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed. Case B : Maximum Power Dissipation (W) 0.8 Normal Voltage = 16V (GPIO = 0V) 1200 19.5 840 Dimming Voltage = 12V (GPIO = 2.8V) 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%. 0.7 0.6 0.5 XDFN/WDFN-8L 2x2 0.4 TSOT-23-6 0.3 0.2 0.1 0 0 Thermal Considerations For continuous operation, do not exceed absolute maximum operation junction temperature. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junction to ambient. The maximum power dissipation can be calculated by following formula: PD(MAX) = ( TJ(MAX) - TA ) / θJA Where T J(MAX) is the maximum operation junction temperature 125°C, TA is the ambient temperature and the θJA is the junction to ambient thermal resistance. For recommended operating conditions specification of RT9285C, where T J (MAX) is the maximum junction DS9285C-03 March 2011 25 50 75 100 125 Ambient Temperature (°C) Figure 6. Derating Curves for RT9285C Packages 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 1µF MLCC capacitor between Pin 6 and Pin 2. } 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) www.richtek.com 9 RT9285C ` 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 RT9285C. ` The embedded antenna is far away and different side RT9285C. ` R1 should be placed as close as RT9285C. ` The through hole of RT9285C's GND pin is recommended as large and many as possible. L1 VIN C1 *1 *2 LX 1 6 VDD GND 2 5 VOUT 3 4 EN C2 *3 GND RSET WLEDs *4 FB EN Figure 7. TOP Figure 8. Bottom www.richtek.com 10 DS9285C-03 March 2011 RT9285C Outline Dimension 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 DS9285C-03 March 2011 www.richtek.com 11 RT9285C D2 D L E2 E 1 e SEE DETAIL A b 2 1 2 1 A A1 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 0.300 0.008 0.012 D 1.950 2.050 0.077 0.081 D2 1.000 1.250 0.039 0.049 E 1.950 2.050 0.077 0.081 E2 0.400 0.650 0.016 0.026 e L 0.500 0.300 0.020 0.400 0.012 0.016 W-Type 8L DFN 2x2 Package www.richtek.com 12 DS9285C-03 March 2011 RT9285C D2 D L E E2 1 e SEE DETAIL A b 2 1 2 1 A A1 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 0.400 0.500 0.016 0.020 A1 0.000 0.050 0.000 0.002 A3 0.102 0.152 0.004 0.006 b 0.200 0.300 0.008 0.012 D 1.950 2.050 0.077 0.081 D2 1.000 1.250 0.039 0.049 E 1.950 2.050 0.077 0.081 E2 0.400 0.650 0.016 0.026 e L 0.500 0.300 0.020 0.400 0.012 0.016 X-Type 8L DFN 2x2 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: 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. DS9285C-03 March 2011 www.richtek.com 13