5A, 18V, 500kHz, ACOT^TM Step-Down Converter

RT6255A/RT6255B

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 R_DS(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^TM) control architecture that provides ultrafast transient response and further reduces the external-component count. In steady states, the ACOT^TM 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.

Applications

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)

Features

Input Supply Voltage Range : 4.5V to 18V
Output Current : 5A
Advanced Constant On-Time (ACOT^TM) 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