RT8477A Datasheet PDF - Richtek

www.Datasheet-PDF.com

RT8477A
Richtek

Part Number RT8477A
Description High Voltage High Current LED Driver
Page 12 Pages


RT8477A datasheet pdf
Download PDF
RT8477A pdf
View PDF for Mobile


No Preview Available !

®
RT8477A
High Voltage High Current LED Driver
General Description
The RT8477A is a current mode PWM controller designed
to drive an external MOSFET for high current LED
applications with wide input voltage (4.5V to 50V) and
output voltage (up to 50V) ranges. With internal 380kHz
operating frequency, the size of the external PWM inductor
and input/output capacitors can be minimized. High
efficiency is achieved by a 100mV current sensing control.
LED Dimming control can be done by analog.
The RT8477A is now available in the SOP-8 (Exposed
Pad) package.
Ordering Information
RT8477A
Package Type
SP : SOP-8 (Exposed Pad-Option 1)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
Features
Buck Constant Current Converter
High Voltage : VIN up to 50V, VOUT up to 50V
380kHz Fixed Switching Frequency
Analog or PWM Control Signal for LED Dimming
Internal Soft-Start to Avoid Inrush Current
Under-Voltage Lockout
Thermal Shutdown
Applications
Desk Lights and Room Lighting
Industrial Display Backlight
Pin Configurations
(TOP VIEW)
VCC
ISP
ISN
VC
8
27
GND
36
9
45
CREG
DRV
SENS
CTL
SOP-8 (Exposed Pad)
Marking Information
RT8477AGSP : Product Number
RT8477A
GSPYMDNN
YMDNN : Date Code
Simplified Application Circuit
VIN
Analog Dimming
C1
R5
RT8477A
VCC
C6
ISP
ISN
CTL DRV
CREG SENS
C2
GND
VC
R1
R4
C5
D1
LEDs
C4
L1
R3
C3
M1
R2
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8477A-01 December 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1



No Preview Available !

RT8477A
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 Positive Input Current Sense.
3 ISN Negative Input Current Sense. Voltage threshold between ISP and ISN is 100mV.
4 VC VC Compensation Node for Current Loop.
5 CTL Analog Dimming Control Input. Effective programming range is 0.33V to 2V.
6
SENS
Current Sense Input for LED Current. Connect the current sense resistor
between external N-MOSFET switch and the ground.
7
DRV
External MOSFET Switch Gate Driver Output.
8
CREG
Regulator Output. Placed 1F capacitor to stabilize the 5V regulator output.
9 (Exposed Pad) GND
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
Function Block Diagram
VCC
CREG
VC
4.5V
OSC
-
+
5V
LDO
Soft-Start
CTL
S
R
R
-
GM
+
+
-
DRV
SENS
ISN
ISP
GND
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
is a registered trademark of Richtek Technology Corporation.
DS8477A-01 December 2014



No Preview Available !

Operation
The RT8477A 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
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 RT8477A provides protection functions which include
over-temperature, and switch current limit to prevent
abnormal situations.
RT8477A
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8477A-01 December 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3



No Preview Available !

RT8477A
Absolute Maximum Ratings (Note 1)
Supply Input Voltage, VCC ------------------------------------------------------------------------------------ 0.3V to 60V
ISP, ISN ------------------------------------------------------------------------------------------------------------ 0.3V to 60V
SENS, DRV, CREG, VC Pin Voltage ----------------------------------------------------------------------- 0.3V to 5.5V
CTL Pin Voltage ------------------------------------------------------------------------------------------------- 0.3V to 20V (Note 2)
Power Dissipation, PD @ TA = 25°C
SOP-8 (Exposed Pad) ----------------------------------------------------------------------------------------- 3.26W
Package Thermal Resistance (Note 3)
SOP-8 (Exposed Pad), θJA ------------------------------------------------------------------------------------ 30.6°C/W
SOP-8 (Exposed Pad), θJC ----------------------------------------------------------------------------------- 3.4°C/W
Junction Temperature ------------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------- 260°C
Storage Temperature Range ---------------------------------------------------------------------------------- 65°C to 150°C
ESD Susceptibility (Note 4)
HBM (Human Body Model) ------------------------------------------------------------------------------------ 2kV
Recommended Operating Conditions (Note 5)
Supply Input Voltage, VCC ------------------------------------------------------------------------------------ 4.5V to 50V
Junction Temperature Range ---------------------------------------------------------------------------------- 40°C to 125°C
Ambient Temperature Range ---------------------------------------------------------------------------------- 40°C to 85°C
Electrical Characteristics
(VCC = 12V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min Typ Max Unit
Overall
Regulator Output Voltage
VCREG
ICREG = 20mA
4.5 5 5.5 V
Supply Current
IVCC
VCTL = 3V
-- --
3 mA
VIN Under Voltage Lockout
Threshold
VUVLO
VIN Rising
VIN Falling
-- 4.25 4.5
-- 4.2 --
V
Current Sense Amplifier
Input Threshold (VISP VISN)
4.5 Common Mode 20V 95 100 105 mV
Input Current
IISP VISP = 24V
IISN VISN = 24V
-- 150 --
-- 50 --
A
Output Current
IVC 2.4V > VC > 0.3V
-- 10 --
A
VC Threshold for CTL Switch Off
-- 0.4 --
V
LED Dimming
Input Current of CTL Pin
ICTL 0.2V VCTL 1.2V
-- 1
2 A
LED Current Off Threshold at CTL VCTL_OFF
-- 0.33 0.4
V
LED Current On Threshold at CTL VCTL_ON
-- 2 2.5 V
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
www.richtek.com
4
is a registered trademark of Richtek Technology Corporation.
DS8477A-01 December 2014



RT8477A datasheet pdf
Download PDF
RT8477A pdf
View PDF for Mobile


Related : Start with RT8477 Part Numbers by
RT8477 High Voltage High Current LED Driver RT8477
Richtek
RT8477 pdf
RT8477A High Voltage High Current LED Driver RT8477A
Richtek
RT8477A pdf

Index :   0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F   G   H   I   J   K   L   M   N   O   P   Q   R   S   T   U   V   W   X   Y   Z   

This is a individually operated, non profit site. If this site is good enough to show, please introduce this site to others.
Since 2010   ::   HOME   ::   Contact