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PDF LED7706 Data sheet ( Hoja de datos )
| Número de pieza | LED7706 | |
| Descripción | 6-rows 30 mA LEDs driver | |
| Fabricantes | STMicroelectronics | |
| Logotipo |  |
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LED7706
6-rows 30 mA LEDs driver with boost regulator
for LCD panels backlight
Features
■ Boost section
– 4.5 V to 36 V input voltage range
– Internal power MOSFET
– Internal +5 V LDO for device supply
– Up to 36 V output voltage
– Constant frequency peak current-mode
control
– 250 kHz to 1 MHz adjustable switching
frequency
– External synchronization for multi-device
application
– Pulse-skip power saving mode at light load
– Programmable soft-start
– Programmable OVP protection
– Stable with ceramic output capacitors
– Thermal shutdown
■ Backlight driver section
– Six rows with 30 mA maximum current
capability (adjustable)
– Rows disable option
– Less than 500 ns minimum dimming on-
time (1 % minimum dimming duty-cycle at
20 kHz)
– ±2 % current matching between rows
– LED failure (open and short-circuit)
detection
Applications
■ LCD monitors and TV panels
■ PDAs panel backlight
■ GPS panel backlight
VFQFPN-24 4x4
Description
The LED7706 consists of a high efficiency
monolithic boost converter and six controlled
current generators (rows) specifically designed to
supply LEDs arrays used in the backlighting of
LCD panels. The device can manage an output
voltage up to 36 V (i.e. 10 white LEDs per row).
The generators can be externally programmed to
sink up to 30 mA and can be dimmed via a PWM
signal (1 % dimming duty-cycle at 20 kHz can be
managed). The device allows to detect and
manage the open and shorted LED faults and to
let unused rows floating. Basic protections (output
over-voltage, internal MOSFET over-current and
thermal shutdown) are provided.
Table 1.
Device summary
Order codes
LED7706
LED7706TR
April 2009
Package
VFQFPN-24 4x4 (exposed pad)
Rev 2
Packaging
Tube
Tape and reel
1/46
www.st.com
46
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1 page  
LED7706
2 Pin settings
2.1 Connections
Figure 2. Pin connection (through top view)
Pin settings
COMP
RILIM
BILIM
FSW
MODE
AVCC
24
1
6
7
LED7706
19
18
OVSEL
PGND
ROW6
ROW5
ROW4
13 ROW3
12
AM00595v1
5/46
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5 Page 
LED7706
Operation description
5.1
5.1.1
Boost section
Functional description
The LED7706 is a monolithic LEDs driver for the backlight of LCD panels and it consists of a
boost converter and six PWM-dimmable current generators.
The boost section is based on a constant switching frequency, peak current-mode
architecture. The boost output voltage is controlled such that the lowest row's voltage,
referred to SGND, is equal to an internal reference voltage (400 mV typ. see Figure 5). The
input voltage range is from 4.5 V up to 36 V. In addition, the LED7706 has an internal LDO
that supplies the internal circuitry of the device and is capable to deliver up to 40 mA. The
input of the LDO is the VIN pin.
The LDO5 pin is the LDO output and the supply for the power MOSFET driver at the same
time. The AVCC pin is the supply for the analog circuitry and should be connected to the
LDO output through a simple RC filter in order to improve the noise rejection.
Figure 4. AVCC filtering
VIN
LDO5
LDO
CLDO5
1uF
Rfilt
4R7 AVCC
CAVCC
100nF
LED7706
SGND
Two loops are involved in regulating the current sunk by the generators.
AM00597v1
The main loop is related to the boost regulator and uses a constant frequency peak current-
mode architecture to regulate the power rail that supplies the LEDs (Figure 5), while an
internal current loop regulates the same current (flowing through the LEDs) at each row
according to the set value (RILIM pin).
Figure 5. Main loop and current loop diagram
VIN
Slope
COMP
LX ROWx
PWM
E/A 0.4V
Error amplifier
Minimum voltage drop
selector
SGND
RILIM
AM00598v1
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11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LED7706.PDF ] | |
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