The RT2858B is a synchronous DC/DC step-down converter with Advanced Constant On-Time (ACOT® ) mode control. It achieves high power density to deliver up to 3A output current from a 4.5V to 18V input supply. The proprietary ACOT® mode offers an optimal transient response over a wide range of loads and all kinds of ceramic capacitors, which allows the device to adopt very low ESR output capacitors for ensuring performance stabilization. In addition, the RT2858B keeps an excellent constant switching frequency under line and load variation and the integrated synchronous power switches with the ACOT® mode operation provides high efficiency in whole output current load range. Cycle-by-cycle current limit provides an accurate protection by a detection of low-side MOSFET and external soft-start setting eliminates input current surge during startup. Protection functions also include output under voltage protection and thermal shutdown.


  • 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
Key Spec.
Status Active
Vin (min) (V) 4.5
Vin (max) (V) 18
Number of Outputs 1
Vout (min) (V) 0.765
Vout (max) (V) 8
Output Adj. Method Resistor
Iout (max) (A) 3
Current Limit (typ) (A) 5
Freq (typ) (kHz) 650
Ext Sync No
Ron_HS (typ) (mOhm) 120
Ron_LS (typ) (mOhm) 50
Iq (typ) (mA) 1
Features ACOT Control;Adjustable Soft-Start;Built-in Bootstrap Switch;Cycle-by-Cycle Current Limit;Enable Input;Fast Transient Response;Force PWM;OCP;OTP;OVP;Stable with Ceramic Capacitor;UVP
Package Type PSOP-8
  • ACOT® Control for Fast Transient, fSW Stability, and Robust Loop Stability with all-MLCC COUT
  • 4.5V to 18V Input Voltage Range
  • 3A Output Current
  • RDSON 120mΩ/50mΩ for High Efficiency Across IOUT Range and Competitive Advantage for IOUT > 1.5A
  • Advanced Constant On-Time Control
  • Support All Ceramic Capacitors
  • Up to 95% Efficiency
  • 650kHz fSW; Start-Up into Pre-Biased Load; Adjustable Soft-Start; Internal Bootstrap
  • Adjustable Output Voltage from 0.765V to 8V
  • Enable; UVLO; OCP (Cycle-by-Cycle); and OTP (150°C)
  • RoHS Compliant and Halogen Free
TitleLast UpdateDownload
3A, 18V, 650kHz ACOT®Synchronous Step-Down Converter2017/08/31
Reference Design
TitleLast UpdateDownload
Richtek Load Transient Tool2022/07/25