RT4503/A
Function Block Diagram
COMP
(RT4503)
V
REF
Internal
OVP
Compensation
Dimming
DAC
LX
+
EA
+
-
Back Light
PWM Logic
FB
-
Slope
OSC
I
SENSE
OCP
GND
I
BIAS
EN
Control Logic
OTP
UVLO
VIN
Operation
The RT4503/A is a constant frequency, current mode
Boost LEDdriver. In normal operation, theN-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.
OCP
The driver provides cycle-by-cycle current limit function
to control the current on power switch.
OVP
The over-voltage protection function monitors the output
voltage via the LX pin voltage. The OVP threshold voltage
is 36V typically. Once the LEDis open, the output voltage
reaches the OVP threshold, the driver will be shut down.
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.
OTP
The over-temperature protection function will shut down
the switching operation when the junction temperature
exceeds 160°C. Once the junction temperature cools
down by approximately 15°C, the converter will
automatically resume switching.
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.
Copyright 2015 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS4503/A-03 June 2015
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
