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RT8477 डेटा पत्रक PDF( Datasheet डाउनलोड )


डेटा पत्रक - High Voltage High Current LED Driver - Richtek

भाग संख्या RT8477
समारोह High Voltage High Current LED Driver
मैन्युफैक्चरर्स Richtek 
लोगो Richtek लोगो 
पूर्व दर्शन
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<?=RT8477?> डेटा पत्रक पीडीएफ

RT8477 pdf
RT8477
Functional Pin Description
Pin No. Pin Name
Pin Function
1 VCC
Supply Voltage Input. For good bypass, a low ESR capacitor is required.
2 ISP
3 ISN
Positive Input Current Sense.
Negative Input Current Sense. Voltage threshold between ISP and ISN is 100mV.
4 CTL
Analog Dimming Control Input. Effective programming range is 0.33V to 2V.
5
SENS
Current Sense Input for LED Current. Connect the current sense resistor between
external N-MOSFET switch and the ground.
6 GND
Ground.
7 DRV
External MOSFET Switch Gate Driver Output.
8 CREG Regulator Output. Placed 1F capacitor to stabilize the 5V regulator output.
Function Block Diagram
VCC
CREG
4.5V
OSC
-
+
5V
LDO
Soft-Start
CTL
S
R
R
-
GM
+
+
-
DRV
SENS
ISN
ISP
GND
Opertation
The RT8477 is a current mode PWM controller designed
to drive an external MOSFET for high current LED
applications. This device 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.
A PWM comparator then turns off the external power
switch when the sensed power switch current exceeds
the internal compensated 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
Copyright ©2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
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 with good dimming
linearity. The max sense threshold of 100mV can be
obtained with CTL pin voltage greater than 2V (max
dimming point). The sense threshold is intentionally forced
to zero by an internal comparator when the CTL pin voltage
is less than around 0.33V (min dimming point). Because
of that, the actual sense threshold right before cut off may
vary from part to part over process variation.
The RT8477 provides protection functions which include
over-temperature, and switch current limit to prevent
abnormal situations.
is a registered trademark of Richtek Technology Corporation.
DS8477-00 December 2013

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डाउनलोड[ RT8477 Datasheet.PDF ]


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