RT2808A 3A, 36V, 500kHz Current Mode Asynchronous Step-Down Converter General Description Features zz z zz 3A Output Current The RT2808A is a current mode asynchronous step-down zz z zz Wide Operating Input Range 5.5V to 36V converter that achieves excellent load and line regulation. zz z zz Adjustable Output Voltage from 1.222V to 26V Over a wide input voltage range from 5.5V to 36V and zz z zz High Efficiency up to 90% supports output current up to 3A. The Current mode zz z zz Internal Compensation Minimizes External Parts operation provides fast transient response and eases loop Count stabilization. zz z zz Internal Soft-Start An adjustable soft-start reduces the stress on the input zz z zz 110m Internal Power MOSFET Switch source at startup. In shutdown mode, the regulator draws zz z zz 25A Shutdown Mode only 25A of supply current. The RT2808A requires a zz z zz Fixed 500kHz Frequency minimum number of readily available external zz z zz Thermal Shutdown components, providing a compact solution. The RT2808A zz z zz Cycle-by-Cycle Current Limit provides protection functions inducing input under voltage zz z zz Available In an SOP-8 (Exposed Pad) Package lockout, cycle-by-cycle current limit, short circuit zz z zz RoHS Compliant and Halogen Free protection and thermal shutdown protection. The RT2808A is available in the SOP-8 (Exposed Pad) Applications package. z Distributive Power Systems z Battery Charger Ordering Information z DSL Modems RT2808A z Pre-regulator for Linear Regulators Package Type SP : SOP-8 (Exposed Pad-Option 2) Marking Information Lead Plating System RT2808AGSP : Product Number G : Green (Halogen Free and Pb Free) RT2808A Note : YMDNN : Date Code GSPYMDNN Richtek products are : RoHS compliant and compatible with the current require- ments of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. Simplified Application Circuit VIN BOOT C V BOOT IN C IN L RT2808A SW V OUT D1 Chip Enable R1 C OUT EN FB GND R2 Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS2808A-00 November 2012 www.richtek.com 1RT2808A Pin Configurations (TOP VIEW) BOOT 8 SW 2 NC 7 VIN GND 3 NC 6 GND 9 4 5 FB EN SOP-8 (Exposed Pad) Functional Pin Description Pin No. Pin Name Pin Function Bootstrap Input for High Side Gate Driver. Connect a 10nF or greater capacitor 1 BOOT from SW to BOOT to power the high side switch. 2, 3 NC No Internal Connection. 4 FB Feedback Input. The feedback threshold is 1.222V. Enable Input. EN is a digital input that turns the regulator on or off. Drive EN 5 EN higher than 1.4V to turn on the regulator, lower than 0.4V to turn it off. For automatic startup, leave EN unconnected. 6, Ground. The exposed pad must be soldered to a large PCB and connected to GND 9 (Exposed Pad) GND for maximum power dissipation. Power Input. A suitable large capacitor should be connected from the VIN to 7 VIN GND to eliminate noise on the input to the IC. Switch Node. Note that a capacitor is required from SW to BOOT to power the 8 SW high side switch. Function Block Diagram VIN Current Sense Amplifier Ramp - Generator + BOOT Oscillator S EN Regulator 500kHz Q Driver + R - Error Reference Current SW Amplifier + Comparator FB - Bootstrap 12k 30pF Control 400k GND 13pF Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS2808A-00 November 2012 2