LED7708 STMicroelectronics, LED7708 Datasheet - Page 18

• Manufacturer Part Number: LED7708
• Description: LED Lighting Drivers 16 Ch 85mA LED 3.6 to 36V 250kHz
• Manufacturer: STMicroelectronics

Specifications of LED7708

• Rohs: yes

Device description
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Device description
The LED7708 is an LED driver that integrates a boost controller, sixteen current generators
and a 4-wire serial interface. It has been specifically designed for driving the LED backlight
in medium to large LCD panels.
The device is controlled by a 4-wire serial interface and can operate both as standalone
driver and as master driver in conjunction with other slave devices.
Basic and advanced dimming functions are supported in order to meet different application
requirements. Regardless of the dimming control technique, the LED7708 can optimize the
power dissipation by controlling the output voltage of the boost converter. Two internal linear
regulators derive the device supply (3.3 V) and the gate driver supply (5 V) from a single
power rail.
Device supply
The LED7708 integrates two low drop-out linear regulators to derive the +3.3 V (typ.) main
supply and the +5 V supply for the gate driver. The VIN pin is the input terminal for both
linear regulators. The output of the 3.3 V LDO is the LDO3 pin, the output of the 5 V LDO is
the VDR pin. The 3.3 V LDO (LDO3 pin) is active if the LREN (linear regulator enable) pin is
left floating or externally set high (see
involved).
The serial interface I/O stage is supplied through the VSI pin. This pin is used to enable the
serial interface and it allows the setting of the logic level of the serial interface signals (3.3 V
or 5 V) at the same time. The serial interface can be powered by the internal 3.3 V LDO (by
simply connecting the LDO3 pin to the VSI pin) or by an external source, usually the same
supply rail as the host controller.
When an external +3.3 V source is available, it is possible to bypass the 3.3 V LDO by
connecting VIN, VDR and LDO3 together to the +3.3 V rail; in this case the gate driver is
supplied at 3.3 V too and a super-logic level MOSFET is required as the power switch.
The 3.3 V regulator is self-protected against overcurrent and thermal damage thanks to a
foldback mechanism. The continuous current capability of the 3.3 V LDO is calculated to not
exceed the junction temperature limit in worst power dissipation conditions.
A 1 µF MLCC on the LDO3 pin is required for ripple filtering and LDO output stability.
The LDO3 pin is internally connected to the undervoltage lockout (UVLO) protection; the
upper and lower UVLO thresholds are reported in
When the voltage at the LDO3 pin falls below the lower UVLO threshold, the device is
turned off (non-latched condition). The device turns on when the voltage at the LDO3 pin
crosses the upper UVLO threshold. Crossing the lower and upper thresholds in sequence
performs the so called “power-on reset” (POR). The POR sequence is used, as well as
toggling the internal DEN bit (see internal registers), when the device is asked to restore
normal operation after a latched fault condition. The 5 V linear regulator, whose output is
connected to the VDR pin, is turned off when the device is disabled, while the 3.3 V linear
regulator is controlled by the LREN pin only.
Doc ID 022698 Rev 1
Section 5: Electrical characteristics
Section 5: Electrical
characteristics.
for the thresholds
LED7708