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


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The RT2859A/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 RT2859A/B are stable with and optimized for ceramic output capacitors.

With internal 70mΩ switches and 70mΩ synchronous rectifiers, the RT2859A/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 lockout, externally-adjustable soft-start, output under- and over-voltage protection, and thermal shutdown provide safe and smooth operation in all operating conditions.

The RT2859A and RT2859B are each available in the WQFN-16L 3x3 package, with exposed thermal pads. The RT2859B switches continuously even at light loads to avoid low-frequency interference while the RT2859A features a power-saving discontinuous operating mode at light loads.


  • Industrial and Commercial Low Power Systems
  • Computer Peripherals
  • LCD Monitors and TVs
  • Green Electronics/Appliances
  • Point of Load Regulation for High-Performance DSPs, FPGAs, and ASICs
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3A, 18V, 650kHz, ACOTTM Synchronous Step-Down Converter2015/12/18
Technical Documents
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Richtek Wide Input Voltage Range DC/DC Power Solutions for Industrial, Automotive and LED lighting applications2020/12/30
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How to estimate control loop bandwidth from the transient response time?2017/03/30 1426
Evaluation Boards
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RT2859BHGQW 3A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter2021/01/21
Reference Design
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Richtek Load Transient Tool2021/01/21
Design Tool
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Richtek Designer™ Web Simulation Tool : RT2859BHGQW2020/09/23
Richtek Designer™ Web Simulation Tool : RT2859BLGQW2020/09/23
Richtek Designer™ Web Simulation Tool : RT2859AHGQW2020/09/23
Richtek Designer™ Web Simulation Tool : RT2859ALGQW2020/09/23
Part NumberPackage TypePackage Qty.Free SampleBuy From Authorized Distributor
RT2859AHGQWWQFN3x3-161500 Not available Buy from Distributor
RT2859ALGQWWQFN3x3-161500 Not available Buy from Distributor
RT2859BHGQWWQFN3x3-161500 Not available Buy from Distributor