LED Driver. RT8474A Datasheet

RT8474A Driver. Datasheet pdf. Equivalent

RT8474A Datasheet
Recommendation RT8474A Datasheet
Part RT8474A
Description High Voltage Multiple-Topology LED Driver
Feature RT8474A; ® RT8474A High Voltage Multiple-Topology LED Driver with Open Detection General Description The RT.
Manufacture Richtek
Datasheet
Download RT8474A Datasheet




Richtek RT8474A
®
RT8474A
High Voltage Multiple-Topology LED Driver
with Open Detection
General Description
The RT8474A is a current-mode LED driver supporting wide
input voltage range from 4.5V to 50V in multiple topologies.
With the internal 500kHz 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
from either analog or PWM signal. The RT8474A provides
an internal soft-start function to avoid inrush current and
thermal shutdown to prevent the device from overheat.
The RT8474A is available in the SOP-8 (Exposed pad)
package.
Features
High Voltage : VIN Up to 50V, VOUT Up to 50V
Support Multiple-Topologies (Buck / Boost / Buck-
Boost)
Built-In 2A Power Switch
Current-Mode PWM Control
500kHz Fixed Switching Frequency
Analog or PWM Control Signal for LED Dimming
Internal Soft-Start to Avoid Inrush Current
OVP Pin for Adjustable OVP Level Protection (for
Buck Only)
Under-Voltage Lockout
Thermal Shutdown
RoHS Compliant and Halogen Free
Ordering Information
RT8474A
Package Type
SP : SOP-8 (Exposed-Option 2)
Note :
Lead Plating System
G : Green (Halogen Free and Pb Free)
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.
Applications
Desk Lights and Room Lighting
Industrial Display Backlight
Marking Information
RT8474A
GSPYMDNN
RT8474AGSP : Product Number
YMDNN : Date Code
Simplified Application Circuit
VIN
Analog Dimming
or PWM Dimming
R5 C1
RT8474A
VCC
C5 ISP
ISN
CTL
R1
R2
C2
SW
VC
CREG
OVP
C3 GND
RSENSE
L1
D1
C4 R4
R3
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS8474A-05 April 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1



Richtek RT8474A
RT8474A
Pin Configurations
(TOP VIEW)
VCC
ISP
ISN
OVP
8
27
GND
36
9
45
CREG
SW
CTL
VC
SOP-8 (Exposed Pad)
Functional Pin Description
Pin No.
1
Pin Name
VCC
Pin Function
Supply Voltage Input. For good bypass, connect a low ESR capacitor
between this pin and GND.
2 ISP
Positive Current Sense Input.
3 ISN
Negative Current Sense Input. Voltage threshold between ISP and ISN is
100mV.
4 OVP
Over-Voltage Protection Sense Input. OVP pin is used for OVP protection
function in buck topology only. The OVP pin must be tied to ISP pin in
boost and buck-boost topologies.
5 VC
Compensation Node for Current Loop.
6 CTL
Analog Dimming Control Input. Effective programming range is 0.2V to
1.2V.
7 SW
8 CREG
9 (Exposed Pad) GND
Switch Node of the PWM Converter.
Regulator Output for Internal Circuit. Place a 1F capacitor to stabilize the
5V output regulator.
Ground. The exposed pad must be soldered to a large PCB and connected
to GND for maximum power dissipation.
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
is a registered trademark of Richtek Technology Corporation.
DS8474A-05 April 2015



Richtek RT8474A
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
3







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