RT8287AZQW Richtek

RT8287A 4A, 21V 500kHz Synchronous Step-Down Converter General Description Features zz z zz 4A Output Current The RT8287A is a synchronous step-down regulator with zz z zz Adjustable Soft-Start an internal power MOSFET. It achieves 4A of continuous zz z zz 120m/40m Internal Power MOSFET Switch output current over a wide input supply range with excellent zz z zz Internal Compensation Minimizes External Parts load and line regulation. Current mode operation provides Count fast transient response and eases loop stabilization. zz z zz Fixed 500kHz Frequency Fault condition protection includes cycle-by-cycle current zz z zz Thermal Shutdown Protection limiting and thermal shutdown. An adjustable soft-start zz z zz Cycle-by-Cycle Over Current Protection reduces the stress on the input source at startup. zz z zz Wide 4.5V to 21V Operating Input Range The RT8287A requires a minimal number of readily zz z zz Adjustable Output from 0.808V to 15V available external components, providing a compact zz z zz Small 14-Lead WDFN Package solution. zz z zz RoHS Compliant and Halogen Free Ordering Information Applications RT8287A z Distributive Power Systems Package Type z Battery Charger QW : WDFN-14L 4x3 (W-Type) z DSL Modems Lead Plating System z Pre-Regulator for Linear Regulators Z : ECO (Ecological Element with Halogen Free and Pb free) Pin Configurations Note : Richtek products are : (TOP VIEW) RoHS compliant and compatible with the current require- 14 VIN 1 AGND 2 13 ments of IPC/JEDEC J-STD-020. SW GND SW 3 12 GND Suitable for use in SnPb or Pb-free soldering processes. 4 11 VCC SW GND 5 10 SS SW 69 BOOT PGOOD 15 EN78 FB Marking Information 01 : Product Code WDFN-14L 4x3 YMDNN : Date Code 01 YM DNN Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS8287A-03 June 2012 www.richtek.com 1RT8287A Typical Application Circuit 1 6 V VIN BOOT IN C C BOOT IN RT8287A 0.1F L 22F 2, 3, 4, 5 V OUT SW 1.2V/4A 9 PGOOD PGOOD R1 R3 R T 100k 8 C OUT FB 11 VCC C SS C C R2 47nF 0.1F 10 SS 7 EN ON/OFF AGND GND 14 12, 13, 15 (Exposed Pad) Table 1. Recommended Components Selection V (V) R1 (k ) R2 (k ) R (k ) L ( H) C (F) OUT T OUT 5 75 14.46 0 4.7 22 x 2 3.3 75 24.32 0 3.6 22 x 2 2.5 75 35.82 0 3.6 22 x 2 1.8 5 4.07 30 2 22 x 2 1.5 5 5.84 39 2 22 x 2 1.2 5 10.31 47 2 22 x 2 1.05 5 16.69 47 1.5 22 x 2 Function Pin Description Pin No. Pin Name Pin Function Supply Input. VIN supplies the power to the IC, as well as the step-down converter 1 VIN switches. Drive VIN with a 4.5V to 21V power source. Bypass VIN to GND with a suitably large capacitor to eliminate noise on the input to the IC. Switch Node. SW is the switching node that supplies power to the output. Connect 2, 3, 4, 5 SW the output LC filter from SW to the output load. Note that a capacitor is required from SW to BOOT to power the high side switch. High Side Gate Drive Boost Input. BOOT supplies the drive for the high side 6 BOOT N-MOSFET switch. Connect a 100nF or greater capacitor from SW to BOOT to power the high side switch. Chip Enable (Active High). For automatic start-up, connect the EN pin to VIN with a 7 EN 100k resistor. Feedback Input. FB senses the output voltage to regulate said voltage. Drive FB 8 FB with a resistive voltage divider from the output voltage. The feedback threshold is 0.808V. Power Good Output. The output of this pin is open-drain. Power good threshold is 9 PGOOD 90% low to high and 70% high to low of regulation value. Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from 10 SS SS to GND to set the soft-start period. Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS8287A-03 June 2012 2