RT8474A datasheet(3/13 Pages) RICHTEK

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RT8474A

DS8474A-05 April 2015

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Function Block Diagram

Operation

The RT8474A can be used in multiple topologies. In Buck

converter applications, an OVP pin is specially designed

to be used for an over voltage protection function.

RT8474A uses a fixed frequency, current-mode control

scheme to provide excellent line and load regulation. The

control loop has a current sense amplifier which senses

the voltage between the ISP and ISN pins and provides an

output voltage at the VC pin. A PWM comparator then

turns off the internal power switch when the sensed power

switch current exceeds the compensated VC pin voltage.

The power switch will not be reset by the oscillator clock

in each cycle. If the comparator does not turn off the

switch in a cycle, the power switch will be on for more

than a full switching period until the comparator is tripped.

In this manner, the programmed voltage across the sense

resistor is regulated by the control loop.

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 CTL pin. The RT8474A

provides protection functions which include over-

temperature, and switch current limit to prevent abnormal

situations.

OSC

4.5V

ISP - 1.2V

ISP

ISN

CTL

VCC

GND

OVP

Soft-Start

LDO

CREG

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