RT2855A/B TM 4A, 18V, 650kHz, ACOT Synchronous Step-Down Converter General Description The RT2855A/B are high-performance 650kHz 4A step- avoid low-frequency interference while the RT2855A down regulators with internal power switches and features a power-saving discontinuous operating mode at synchronous rectifiers. They feature quick transient light loads. response using their Advanced Constant On-Time TM (ACOT ) control architecture that provides stable Features operation with small ceramic output capacitors and without Fast Transient Response complicated external compensation, among other benefits. Steady 650kHz Switching Frequency at all Load The input voltage range is from 4.5V to 18V and the output Current (RT2855B) is adjustable from 0.765V to 7V. Discontinuous operating mode at Light Load TM (RT2855A) The proprietary ACOT control improves upon other fast- 4A Output Current response constant on-time architectures, achieving nearly TM Advanced Constant On-Time (ACOT ) Control constant switching frequency over line, load, and output Optimized for Ceramic Output Capacitors voltage ranges. Since there is no internal clock, response 4.5V to 18V Input Voltage Range to transients is nearly instantaneous and inductor current Internal 70m Switch and 30m Synchronous can ramp quickly to maintain output regulation without Rectifier large bulk output capacitance. The RT2855A/B are stable 0.765V to 7V Adjustable Output Voltage with and optimized for ceramic output capacitors Externally-adjustable, Pre-biased Compatible Soft- With internal 70m switches and 30m synchronous Start rectifiers, the RT2855A/B display excellent efficiency and Cycle-by-Cycle Current Limit good behavior across a range of applications, especially Optional Output Discharge Function for low output voltages and low duty cycles. Cycle-by- Output Over- and Under-voltage Shut-down cycle current limit, input under-voltage lock-out, externally- Latched (RT2855ALGQW/RT2855BLGQW Only) adjustable soft-start, output under- and over-voltage Hiccup Mode (RT2855AHGQW/RT2855BHGQW protection, and thermal shutdown provide safe and smooth Only) operation in all operating conditions. Input Under Voltage Lockout The RT2855A and RT2855B are each available in Thermal Shutdown WQFN-16L 3x3 package, with exposed thermal pads. The RT2855B switches continuously even at light loads to Simplified Application Circuit RT2855A/B V VIN IN V SW OUT VCC BOOT Power Good VS PGOOD VREG5 FB Input Signal EN SS VREG5 GND PGND Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS2855A/B-00 March 2015 www.richtek.com 1RT2855A/B Applications Ordering Information RT2855A/B Industrial and Commercial Low Power Systems Computer Peripherals Package Type QW : WQFN-16L 3x3 (W-Type) LCD Monitors and TVs Green Electronics/Appliances Lead Plating System G : Green (Halogen Free and Pb Free) Point of Load Regulation for High-Performance DSPs, FPGAs, and ASICs H : Hiccup Mode OVP & UVP L : Latched OVP & UVP A : PSM Marking Information B : PWM RT2855AHGQW Note : 4G= : Product Code Richtek products are : YMDNN : Date Code 4G=YM RoHS compliant and compatible with the current require- DNN ments of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. RT2855ALGQW 4F= : Product Code Pin Configurations YMDNN : Date Code 4F=YM (TOP VIEW) DNN 16 15 14 13 RT2855BHGQW 1 12 FB BOOT VREG5 2 11 4E= : Product Code SW GND 3 10 SS SW YMDNN : Date Code 17 4E=YM 4 9 GND SW DNN 5 6 7 8 RT2855BLGQW 4D= : Product Code WQFN-16L 3x3 YMDNN : Date Code 4D=YM DNN Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS2855A/B-00 March 2015 2 PGOOD VS EN VCC PGND VIN PGND VIN