brled770x

LED7706/7/8
LED drivers for backlighting and lighting applications
www.st.com/led
Content
Advanced power management to drive LEDs ........................ 3
LED7706/7: six rows of up to 10 white LEDs, with adjustable
maximum current.....................................................................................3
Key features.........................................................................................3
Key benefits.........................................................................................3
Targeted applications...........................................................................3
Application diagram..............................................................................4
LED7706/7 product table.....................................................................4
Evaluation boards ................................................................................4
LED7708: 16-channel, 85 mA LED driver with boost controller and
4-wire serial interface...............................................................................5
Key features ........................................................................................5
Key benefits .........................................................................................5
Targeted applications...........................................................................5
Application diagram..............................................................................6
LED7708 product table........................................................................6
Evaluation boards ................................................................................6
LED7708 application example: RGGB Backlight...................................7
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Advanced power management to drive LEDs
STMicroelectronics, a world leader in power management solutions, leveraging its leading-edge expertise in
power technologies, offers complete solutions to drive LEDs in a variety of applications.
The LED770x family is composed of three monolithic, high-efficiency LED drivers intended for arrays used in
the backlight of LCD panels in consumer, industrial and automotive applications, and in architectural lighting
applications.
Housed in compact QFN packages, the ICs integrate a boost converter and a LED array driver consisting
of several PWM-dimmable current generators giving excellent dimming performances, suitable for all LCD
backlighting applications.
The boost converter is based on a constant switching-frequency, peak current-mode architecture. The devices
keep the lowest row’s voltage regulated at the internal reference voltage, and adapt the boost output voltage to
reduce power losses across the current generators. The boost-converter default switching frequency is fixed
at about 650 kHz. This is a good compromise in terms of efficiency, size and cost of the power elements and of
the overall application, but it can also be set anywhere in the 250 kHz to 1 MHz range by simply connecting an
external resistor, if more flexibility is required.
The LED770x family, with an input voltage range from 3.6 V or 4.5 V up to the output voltage, covers the most
common voltage buses (5 V, 12 V and 24 V). Additional flexibility is guaranteed by a full set of adjustable
protection functions, together with complete and flexible fault management, a wide input voltage range and high
switching frequency, to reduce the size and cost of the total application.
LED7706/7: six rows of up to 10 white LEDs, with adjustable
maximum current
Downstream from the boost converter stage, the LED7706 and LED7707 have six controlled-current generators (rows) that are
externally programmable to sink up to 30 mA (LED7706) and 85 mA (LED7707) and can be dimmed via a PWM signal.
In the LED7707, the six lines may also be put in parallel to drive a single LED string to a total current in excess of 500 mA.
The devices can manage an output voltage of up to 36 V powering up to 10 white LEDs per row.
Row failures (open and shorted LEDs) are detected and managed in a safe way and basic protection of the power stage
(output overvoltage, internal MOSFET overcurrent and thermal shutdown) are provided.
The devices are housed in small VFQFPN4x4-24L packages.
Key features
Boost controller
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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 currentmode control
250 kHz to 1 MHz adjustable
switching frequency
External synchronization for multidevice application
Pulse-skip power saving mode at
light load
Programmable soft-start
Programmable OVP protection
Stable with ceramic output
capacitors
Thermal shutdown
Backlight driver
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Six rows up to 10 white LEDs each,
with adjustable maximum current:
QQ 30 mA max for LED7706
QQ 85 mA max for LED7707
Rows disable option
Less than 10 μs minimum dimming
on-time for LED7707, 500 ns for
LED7706
±2 % current matching between rows
LED failure (open and short-circuit)
detection
Key benefits
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Monolithic and flexible solution
High efficiency
Superior dimming capability
Complete and flexible fault
management
Targeted applications
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Consumer: small to mid size LCD
TVs, monitors
Automotive: navigation displays and
dashboards
Industrial: lighting, displays,
e-signage
VFQFPN-24 4x4
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Application diagram
VIN
AVCC
VIN
LX
SLOPE OVSEL
FSW
LDO5
ROW0
BILIM
ROW1
ROW2
RILIM
LED7706
SS
ROW3
COMP
ROW4
SGND
ROW5
DIM
FAULT
EN
SYNC MODE PGND
Up to 10 WLEDs per row
Dimming
Fault
Faults management selection
Enable
Sync output
LED7706/7 product table
Part number
LED7706
LED7707
VIN (V)
4.5 to 36
4.5 to 36
VOUT (V)
Up to 36
Up to 36
Irows (mA)
Up to 30
Up to 85
Rows
6
6
Min dimming time
500 ns
10 μs
Max LEDs per row
10 (white)
10 (white)
Fsw (kHz)
200 to 1000
200 to 1000
Package
VFQFPN4x4-24L
VFQFPN4x4-24L
Evaluation boards
Part number
STEVAL-ILL020V1
STEVAL-ILL021V1
STEVAL-ILL020V1
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Description
LED7706: 6-row, 30 mA LED driver with boost converter
LED7707: 6-row, 85 mA LED driver with boost converter
STEVAL-ILL021V1
Related documentation
AN2809
AN2810
LED7708: 16-channel, 85 mA LED driver with boost controller and
4-wire serial interface
The LED7708 has been specifically designed to supply several LEDs from a single low-voltage rail in order to address TV and
monitor backlights, medium- and large-size LCD panel backlights and RGB/RGGB backlight applications.
It has sixteen current generators rated at 40 V and a 4-wire serial interface to control LED brightness.
These channels can be put in parallel for higher output currents. A selectable 12-bit or 16-bit gray-scale brightness control
allows independent PWM on each channel.
A programmable on-chip dimming oscillator is provided to simplify external circuitry. The device has dedicated pins to lock
synchronize with other devices (master or slave) for noise reduction in multi-device applications.
The LED7708 implements basic protection (OVP, OCP and thermal shutdown), as well as LED-array protection. It can detect
and manage open-LED and shorted-LED faults, and different fault management options are available in order to cover most
application needs.
Key features
Key benefits
Targeted applications
Boost controller section
Advanced power management
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3.6 V to 36 V input voltage range
(with internal LDOs)
Adaptive output voltage
OVP, OCP and thermal protection
External synchronization for multidevice applications
Over-temperature alert and thermal
shutdown
LED array driver section
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16 paralleable channels with 85
mA/ch current capability
±2% channel current accuracy (full
range)
±2% max channel-to-channel
current matching
4% max chip-to-chip current
accuracy
LED short-circuit and open-channel
fault detection and disconnection
4 wire, 30 MHz serial interface
16x 16-bit, 1x 256-bit or 1x 192-bit
serial data format
12/16-bit resolution PWM dimming
on each channel
Programmable internal dimming
oscillator
128-step overall current generator
adjustment
Minimizes overall system power
dissipation and maximizes efficiency
Advanced control of color and
brightness
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TV and monitor backlight units for
LCD panels
Medium- and large-size LCD panel
backlighting
RGB/RGGB backlight solutions
Individual PWMs give independent
control of average current in
each string, adjusting brightness
mismatches among the LED strings
in synergy with programmable current
generators to provide best color and
brightness uniformity
Advanced backlight features
The advanced features enable it
to support both local dimming and
scanning backlights, and enhanced
active LED fault management allows
real-time status monitoring to prevent
backlight damage through automatic
string disconnection
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Application diagram
VIN
VOUT
VFQFPN-48 7x7
Serial interface
LED7708
Handshake
signals
LED7708 product table
Part number
LED7708
VIN (V)
VOUT (V)
ICH (mA)
Channels
Interface
Local dimming
ICH adj
Package
3.6 to 36
Up to 60
Up to 85
16
4-wire SI
12/16-bit PWM
200 to 1000
VFQFPN-48 7x7
Evaluation boards
Part number
STEVAL-ILL035V1
STEVAL-ILL035V2
STEVAL-ILL035V1 (master)
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Description
LED7708 16-row, up to 85 mA master board LED driver with boost converter
LED7708 16-row, up to 85 mA slave board LED driver
STEVAL-ILL035V2 (slave)
Related documentation
LED7708 application example: RGGB Backlight
Backlight module example:
4 strings of 4 LEDs (RGGB)
(75 mA rated LEDs)
75 mA
75 mA
75 mA
LED7708
LED7708
LED7708
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© STMicroelectronics - February 2012 - Printed in United Kingdom - All rights reserved
The STMicroelectronics corporate logo is a registered trademark of the STMicroelectronics group of companies
All other names are the property of their respective owners
Order code: BRLED770X0112
For more information on ST products and solutions, visit www.st.com
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