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PDF RT8491 Data sheet ( Hoja de datos )
| Número de pieza | RT8491 | |
| Descripción | High Voltage 6-CH LED Driver Controller | |
| Fabricantes | Richtek | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de RT8491 (archivo pdf) en la parte inferior de esta página. Total 21 Páginas | ||
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®
RT8491
High Voltage 6-CH LED Driver Controller
General Description
The RT8491 is a 6-CH LED driver controller that delivers
well matched LED current to each channel of LED string.
With external current sources, the number of LEDs per
string is only limited by the current source and the VIN/
VOUT conditions. The current mode PWM boost type
controller operates at a programmable switching
frequency of up to 1MHz, with a wide VIN range covering
from 9V to 32V. The switch driver is designed to drive
industrial grade high power MOSFETs.
The PWM loop selects and regulates the LED string with
the highest voltage string to 0.9V, thus allowing voltage
mismatches between the LED strings. The RT8491
automatically detects and excludes any open and/or
broken strings during operation from the PWM loop to
prevent VOUT from over voltage.
The RT8491 also provides LED short protection. If LED
short occurs and causes any LEDx but not all LEDx pin
voltage greater than 8V, the CAP pin is charged up by
internal 10μA. If the LED short condition lasts longer than
the CAP pin voltage reaches 3.5V, the FLAG pin will go
high and the GATE pin will be kept low immediately until
the CAP pin voltage drops below 3.5V. The delay time is
programmable by the capacitor at the CAP pin.
Features
Wide Operation Voltage Range : 9V to 32V
Programmable Channel Current
3% Current Matching Accuracy between Channels
Programmable Switching Frequency
Easy Analog and Digital Dimming Control
Programmable Soft-Start
LED Open Channel Detection and Protection
LED Short-Fault Detect Latch Off Multiple LED
Strings
Programmable Output Over Voltage Protection
Under Voltage Lockout and Thermal Shutdown
32-Lead WQFN Package
Applications
Building and Street Lighting
LED TV Backlight
LED Monitor Backlight
Industrial Display Backlight
Simplified Application Circuit
VIN
R3
12V
CIN
CVCC
CB
RT8491
VCC
CAP
VBASE
GBIAS
GATE
ISENSE
RSET
RSET
SS
CSS
GND
Chip Enable
EN
ACTL
LED1
GATE1
SENSE1
LED6
GATE6
SENSE6
L1 D1
CT
MSW
RSENSE
COUT
…
M1
RS1
VOUT
6 x N LEDs
M6
RS6
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8491-04 October 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
Operation
The internal gate driver circuit is powered from GBIAS pin
around 10V (10.7V − VBE). The GBIAS voltage is
generated by an internal base driver to drive an external
NPN emitter follower. The OSC block generates a
programmable frequency which is set by an external
resistor at RSET pin for RT8491 operation. At the
beginning of the oscillator cycle, the GATE turns high.
The VOUT regulation unit automatically detects the lowest
sensed LEDx pin feedback voltage among the 6 LED
strings and compares to 0.9V. If the lowest LEDx pin
voltage is lower than 0.9V, the VC pin (the output of the
OP AMP in VOUT regulation unit) is charged high. The
ISENSE pin voltage is the triangular feedback signal of
the sensed switch current (which equals inductor current
ramp). The PWM comparator compares ISENSE pin
voltage to VC pin voltage. When ISENSE pin voltage
exceeds VC pin voltage, the PWM comparator resets the
latch and turns off GATE. If ISENSE pin voltage does
exceed VC pin voltage by the end of the switching cycle,
the GATE will be turned off for minimum off time. The cycle
RT8491
repeats when the GATE is turned on at the beginning of
the next switching cycle. By this PWM closed loop control,
the lowest sensed LEDx pin voltage among the 6 LED
strings is regulated to 0.9V.
As the system starts, the cap at the soft start pin is slowly
charged up by an internal current source around 10μA.
During soft start period, the VC pin voltage follows soft
start pin voltage up by one VBE and gradually ramps up.
The slowly rising VC pin voltage allows the PWM duty to
increase gradually to achieve soft start function.
The dimming can be done by varying ACTL pin analog or
PWM voltage signal. The internal sense threshold for the
6 current sources follows ACTL signal to achieve dimming
control.
The fault protection features of RT8491 include (1) Input
Under Voltage Lockout (UVLO), (2) VOUT Over Voltage
Protection (OVP), (3) LED string short, (4) LED string
open, and (5) Over Temperature Protection (OTP).
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8491-04 October 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
RT8491
Shutdown Current vs. Input Voltage
8
7
6
5
4
3
2
1
VIN = 8V to 36V
0
8 12 16 20 24 28 32 36
Input Voltage (V)
GATE Voltage vs. Input Voltage
10
9
8
7
6
5
4
8 12 16 20 24 28 32 36
Input Voltage (V)
Switching Frequency vs. Input Voltage
320
300
280
260
240
220
8
RSET = 39kΩ
12 16 20 24 28 32 36
Input Voltage (V)
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8491-04 October 2014
Shutdown Current vs. Temperature
6
5
4
3
2
1
0
-50
-25
0 25 50 75 100 125
Temperature (°C)
GATE Voltage vs. Temperature
12
10
8
6
4
2
-50
-25
VCC = 12V
0 25 50 75 100 125
Temperature (°C)
Switching Frequency vs. Temperature
320
300
280
260
240
220
-50
-25
RSET = 39kΩ
0 25 50 75 100 125
Temperature (°C)
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet RT8491.PDF ] | |
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