RT9741

2

DS9741-01 March 2015

www.richtek.com

©

Copyright 2015 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

Function Block Diagram

Functional Pin Description

Pin No.

Pin Name

Pin Description

1

VIN

Power Input.

2

VOUT

Output Voltage.

3

GND

Ground.

Output Voltage

Detection

Gate

Control

VOUT

Charge

Pump

VIN

Bias

GND

Current

Limiting

Auto

Discharge

UVLO

Thermal

Protection

Oscillator

Pin Configurations

(TOP VIEW)

SOT-23-3

VIN

VOUT

GND

2

3

Operation

Charge Pumps and Drivers

An internal charge pump supplies power to the driver circuit

and provides the necessary voltage to pull the gate of the

MOSFET above the source. The driver controls the gate

voltage of the power switch.

Current Limit

The RT9741 continuously monitors the output current for

over-current protection to protect the system power, the

power switch, and the load from damage during output

short circuit. When an overload or short circuit occurs,

the current-sense circuitry sends a control signal to the

driver. The driver reduces the gate voltage and drives the

power MOSFET into its saturation region, which switches

the output into a constant-current mode and holds the

current constant until the thermal shutdown occurs or the

fault is removed.

Under-Voltage Lockout

A voltage-sense circuit monitors the input voltage. When

the input voltage is below approximately 1.3V, UVLO turns

off the MOSFET switch.

Thermal Shutdown

The RT9741 continuously monitors the operating

temperature of the power switch for over-temperature

protection. The RT9741 turns off the power switch to

prevent the device from damage if the junction temperature

rises to approximately 120

°C due to over-current or short-

circuit conditions.

The pass element turns on again after the junction

temperature cools to 80

°C. The

RT9741 lowers its OTP trip level from 120

°C to 100°C

when output short circuit occurs (V