RT4533 datasheet(3/11 Pages) RICHTEK

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RT4533/A

DS4533/A-02

September 2015

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Function Block Diagram

Operation

The RT4533/A is a constant frequency, current mode

Boost LED driver. In normal operation, the N-MOSFET is

turned on when the PWM Control circuit is set by the

oscillator and is turned off when the current comparator

resets the PWM Control circuit. While the N-MOSFET is

turned off, the inductor current conducts through the

external diode.

UVLO

When the input voltage is lower than the UVLO threshold

(2.37V typ.), the driver will turn off. There is a 80mV for

the UVLO hysteresis control.

Soft-Start

When the device is enabled, the Comp ramps up to the

target voltage in a specific time. This ensures that the

output voltage rises slowly to reduce the input inrush

current.

EN Dimming

The EN pin is used for the control input for both PWM

dimming mode and digital dimming mode. Shutdown delay

when the EN voltage is logic low for more than specific

time, the driver will be shut down.

Logic Control,

Minimum On

Time

Current-

Sense

OCP

Driver

Slope

Compensation

PWM

LPF

20ms

Shutdown

Enable

Logic

OVP

OTP

UVLO

VREF

GND

VOUT

VIN

Internal

Compensation

Internal

Soft-Start

PWM

Oscillator

Reference

Voltage

Bias

Current

OCP

The driver provides cycle-by-cycle current limit function

to control the current on power switch. The boost switch

turns off when the inductor current reaches this current

threshold and it remains off until the beginning of the next

switching cycle. This protects the RT4533/A and external

component under overload conditions.

OVP

The Over Voltage Protection is detected by a resistor

divider circuit from VOUT.

Once VOUT goes over the OVP voltage, LX pin stops

switching and the power N-MOSFET will be turned off.

Then, the VOUT will be discharged by external resistor.

OVP will be released until EN goes from Lo to Hi again.

OTP

As the die temperature is higher than 160

°C, the chip

also will enter protection mode. The power MOSFET will

be turned off during protection mode to prevent abnormal

operation. The device is released from shutdown

automatically when the junction temperature decreases

by 15

°C.

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