3A, 18V, 650kHz, ACOT® Synchronous Step-Down Converter


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The RT2853A/B are high-performance 650kHz 3A step-down regulators with internal power switches and synchronous rectifiers. They feature quick transient response using their Advanced Constant On-Time (ACOT®) control architecture that provides stable operation with small ceramic output capacitors and without complicated external compensation, among other benefits. The input voltage range is from 4.5V to 18V and the output is adjustable from 0.765V to 7V.

The proprietary ACOT® control improves upon other fast-response constant on-time architectures, achieving nearly constant switching frequency over line, load, and output voltage ranges. Since there is no internal clock, response to transients is nearly instantaneous and inductor current can ramp quickly to maintain output regulation without large bulk output capacitance. The RT2853A/B are stable with and optimized for ceramic output capacitors.

With internal 110mΩ switches and 30mΩ synchronous rectifiers, the RT2853A/B display excellent efficiency and good behavior across a range of applications, especially for low output voltages and low duty cycles. Cycle-by-cycle current limit, input under-voltage lock-out, externally-adjustable soft-start, output under- and over-voltage protection, and thermal shutdown provide safe and smooth operation in all operating conditions.

The RT2853A and RT2853B are each available in WQFN-16L 3x3 package, with exposed thermal pads.


  • Industrial and Commercial Low Power Systems
  • Computer Peripherals
  • LCD Monitors and TVs
  • Point of Load Regulation for High-Performance DSPs, FPGAs, and ASICs
Key Spec.
RT2853A RT2853B
Status Active Active
Vin (min) (V) 4.5 4.5
Vin (max) (V) 18 18
Number of Outputs 1 1
Vout (min) (V) 0.765 0.765
Vout (max) (V) 7 7
Output Adj. Method Resistor Resistor
Iout (max) (A) 3 3
Current Limit (typ) (A) 4.5 4.5
Freq (typ) (kHz) 650 650
Ext Sync No No
Ron_HS (typ) (mOhm) 110 110
Ron_LS (typ) (mOhm) 30 30
Iq (typ) (mA) 1 1
Features ACOT Control;Adjustable Soft-Start;COT Control;Cycle-by-Cycle Current Limit;Enable Input;Fast Transient Response;OCP;OTP;OVP;PSM;Power Good;SCP;Stable with Ceramic Capacitor;UVP ACOT Control;Adjustable Soft-Start;COT Control;Cycle-by-Cycle Current Limit;Enable Input;Fast Transient Response;OCP;OTP;OVP;Power Good;SCP;Stable with Ceramic Capacitor;UVP
Package Type WQFN3x3-16 WQFN3x3-16
  • Fast Transient Response
  • Steady 650kHz Switching Frequency
  • Enhanced Efficiency at Light Load (RT2853A)
  • Advanced Constant On-Time (ACOT®) Control
  • Optimized for Ceramic Output Capacitors
  • 4.5V to 18V Input Voltage Range
  • Internal 110mΩ Switch and 30mΩ Synchronous Rectifier
  • 0.765V to 7V Adjustable Output Voltage
  • Externally-adjustable, Pre-biased Compatible Soft-Start
  • Cycle-by-Cycle Current Limit
  • Optional Output Discharge Function
  • Output Over- and Under-voltage Shut-down
    ► Latched (RT2853ALGQW/RT2853BLGQW Only)
    ► With Hiccup Mode (RT2853AHGQW/
    RT2853BHGQW Only)
TitleLast UpdateShareDownload
3A, 18V, 650kHz, ACOT® Synchronous Step-Down Converter2013/07/02
Technical Documents
TitleLast UpdateShareDownload
ACOT® Stability Testing2022/09/06
Buck Converter Selection Criteria2022/09/06
Comparing Buck Converter Topologies2022/09/06
The Calculation of Output DC Offset for ACOT™ Control Buck Converter with Feed-forward Compensator2022/09/05
ACOT™ (Advanced Constant-On Time) Synchronous Step-Down Converters [Oct., 2015]2022/09/04
Richtek Selection Guide [Oct., 2021]2022/09/03
TitleLast UpdateShareViews
How to estimate control loop bandwidth from the transient response time?2017/03/30 1570
Introduction to Richtek's Advanced Constant On Time Buck Converters2013/05/14 87
Evaluation Boards
TitleLast UpdateShareDownload
RT2853BHGQW 3A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter2021/01/21
Reference Design
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Richtek Load Transient Tool2022/07/25
Design Tool
TitleLast UpdateShare
Richtek Designer™ Web Simulation Tool : RT2853AHGQW2022/04/22
Richtek Designer™ Web Simulation Tool : RT2853ALGQW2022/04/22
Richtek Designer™ Web Simulation Tool : RT2853BHGQW2022/04/22
Richtek Designer™ Web Simulation Tool : RT2853BLGQW2022/04/22
Part NumberPackage TypePackage Qty.Free SampleBuy From Authorized Distributor
RT2853AHGQWWQFN3x3-161500 Not available Not available
RT2853ALGQWWQFN3x3-161500 Not available Not available
RT2853BHGQWWQFN3x3-161500 Request Not available
RT2853BHGQWWQFN3x3-161500 Request Buy from Distributor
RT2853BLGQWWQFN3x3-161500 Not available Not available