RT8498

2

DS8498-01 April 2017

www.richtek.com

©

Copyright 2017 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

Functional Block Diagram

Functional Pin Description

Pin No.

Pin Name

Pin Function

1

SW

Switch node of the PWM converter.

2

GND

Ground.

3

DCTL

Digital dimming control input.

4

ACTL

Analog dimming control input. Effective programming range is 0.65V to 1.2V.

5

VCC

Supply voltage input. For good bypass, connect a low ESR capacitor between this

pin and GND.

6

ISN

Current sense input. Voltage threshold between VCC and ISN is 100mV.

R

R

S

OSC

+

-

2.5V

0.65/0.2V

+

-

1.2V

+

-

Shutdown

+

-

GM

VCC

ISN

DCTL

ACTL

VCC

SW

GND

Soft-Start

DCTL

+

-

Operation

The RT8498 is specifically designed to be operated in

Buck, Boot and Buck-Boost converter applications. This

device uses a fixed frequency, current-mode control

scheme to provide excellent line and load regulation. The

maximum duty ratio of the RT8498 is 100% (typ.), and

the minimum on time is 150ns (typ.)

The current through the sense resistor is set by the

programmed voltage and the sense resistance. The voltage

across the sense resistor can be programmed by the

analog or digital signal at the ACTL pin. By adding a 0.47

μF

filtering capacitor on the ACTL pin, the PWM dimming

signal on DCTL pin will be averaged and converted into

0.55 x PWM dimming duty ratio. The RT8498 provides

protection functions which include over- temperature, and

switch current limit to prevent abnormal situations.