RT8474A Datasheet, PDF (3/13 Pages) Richtek Technology Corporation – High Voltage Multiple-Topology LED Driver

Function Block Diagram
VCC
OVP
-
4.5V +
-
ISP - 1.2V +
OSC S
R
R
RT8474A
SW
5V
LDO
CREG
VC
Soft-Start
-
GM
+
+
-
ISN
ISP
GND
CTL
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.
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS8474A-05 April 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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