RT8457A Datasheet, PDF (1/11 Pages) Richtek Technology Corporation – Isolated Secondary-Side LED Lighting Dimmable Current Controller

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RT8457A
Isolated Secondary-Side LED Lighting Dimmable Current
Controller
General Description
The RT8457A is an isolated secondary LED current
controller designed specifically for lighting fixtures such
as E27, GU10, T5 and T8 that require power line isolation
for safety and reliability, and that require high conversion
efficiency as well as high LED current accuracy.
The RT8457A contains 1) a constant current regulating
amplifier with 170mV threshold used to program the LED
string current with a simple resistor to within 5% LED
current accuracy; 2) an over-voltage comparator to protect
the output when LED string is open or broken; and 3) an
opto-coupler driver to control the primary-side of the
transformer to complete the system loop.
Precise dimming is achieved by controlling the LED current
at the secondary-side via analog dimming. Applying a
voltage greater than 1.1V at the ACTL pin will set the LED
current sense threshold between the LED and GND pins
at the highest level (around 170mV). The maximum LED
current is adjustable by the sense resistor between the
LED and GND pins. Lowering the ACTL pin voltage will
reduce the LED current sense threshold.
The RT8457A is available in the SOP-8 package.
Features
z Secondary-Side LED Current Regulation
z High Accuracy 170mV LED Current Threshold
Control
z 0.5mA Operating Current
z Adjustable LED Current
z Precision Secondary-Side LED Current Dimming
z Precision Analog Dimming at Secondary-Side
z Output Over-Voltage Protection
z SOP-8 Package
z RoHS Compliant and Halogen Free
Applications
z Isolated LED Lighting Fixtures
z E27/GU10/T5/T8 LED Lamp
Marking Information
RT8457A
GSYMDNN
RT8457AGS : Product Number
YMDNN : Date Code
Simplified Application Circuit
D1
Secondary-Side
Winding
Opto-Coupler
C1
VCC
REF
OUT
C2
RT8457A
OVP
Dimming
Control
ACTL
GND
LED
R_{LED R1}
R2
R_S
V_OUT
LED String
Copyright ©2013 Richtek Technology Corporation. All rights reserved.
DS8457A-02 September 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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