The RT6255A/B is a high-performance, synchronous step-down DC-DC converter that can deliver up to 5A output current from a 4.5V to 18V input supply. The device integrates low RDS(ON) power MOSFETs, accurate 0.6V reference and an integrated diode of bootstrap circuit to offer a very compact solution.

The RT6255A/B adopts Advanced Constant On-Time (ACOT®) control architecture that provides ultrafast transient response and further reduces the external-component count. In steady states, the ACOT® operates in nearly constant switching frequency over line, load and output voltage ranges and makes the EMI filter design easier.

The device offers Independent enable control input pin and power good indicator (TSOT23-8 only) for easily sequence control. To control the inrush current during the startup, the device provides a fixed 1.5ms soft-start up. Fully protection features are also integrated in the device including the cycle-by-cycle current limit control, UVP, input UVLO and OTP.

The RT6255A/B is available in the TSOT-23-6 (FC) and TSOT-23-8 (FC) package.


  • Set Top Box
  • Portable TV
  • Access Point Router
  • DSL Modem
  • LCD TV
Key Spec.
RT6255A RT6255B
Status Active Active
Vin (min) (V) 4.5 4.5
Vin (max) (V) 18 18
Number of Outputs 1 1
Vout (min) (V) 0.6 0.6
Vout (max) (V) 5 5
Output Adj. Method Resistor Resistor
Iout (max) (A) 5 5
Current Limit (typ) (A) 7.25 7.25
Freq (typ) (kHz) 500 500
Ext Sync No No
Ron_HS (typ) (mOhm) 45 45
Ron_LS (typ) (mOhm) 23 23
Iq (typ) (mA) 0.115 0.115
Features ACOT Control;Cycle-by-Cycle Current Limit;Enable Input;Fast Transient Response;OTP;PSM;Power Good;SCP;Stable with Ceramic Capacitor;UVP ACOT Control;Cycle-by-Cycle Current Limit;Enable Input;Fast Transient Response;OTP;PSM;Power Good;SCP;Stable with Ceramic Capacitor;UVP
Package Type TSOT-26(FC);TSOT-28(FC) TSOT-26(FC);TSOT-28(FC)
  • Input Supply Voltage Range : 4.5V to 18V
  • Output Current : 5A
  • Advanced Constant On-Time (ACOTTM) Control for Ultrafast Transient Response
  • Steady Switching Frequency : 500kHz
    ► Forced PWM Mode (RT6255B)
    ► Pulse-Skipping Mode (PSM) at Light Load (RT6255A)
  • Optimized for Low-ESR Ceramic Output Capacitors
  • Programmable Output Voltage : 0.6V to 5V
  • Internal 45mΩ Switch and 23mΩ Synchronous Rectifier
  • Cycle-by-Cycle Current Limit Protection
  • Internal Soft-Start (Typ 1.5ms) or Externally Adjustable, Pre-biased Compatible Soft-Start (Only for Option with SS Pin)
  • Power Good Indicator (90%) (Only for Option with PGOOD Pin)
  • Output Under-Voltage Protection (UVP)
  • Over-Temperature Protection (OTP)
  • Input Under-Voltage Lockout (UVLO)
  • Available in TSOT-23-6 (FC) and TSOT-23-8 (FC) Packages
TitleLast UpdateDownload
5A, 18V, 500kHz, ACOTTM Step-Down Converter2016/08/30
Technical Documents
TitleItem TypeLast UpdateDownload
Richtek Product Selection Guide [Jan., 2024] Selection Guide2024/01/18
Richtek Featured Product Tree [Aug., 2023] Selection Guide2023/08/07
Part NumberPackage TypePackage Qty.Free SampleBuy From Authorized Distributor
RT6255AHGJ6FTSOT-26(FC)3000 Request Buy from Distributor
RT6255BHGJ6FTSOT-26(FC)3000 Request Buy from Distributor
RT6255BHGJ8FTSOT-28(FC)3000 Request Buy from Distributor