LP8861-Q1 Datasheet, PDF (11/43 Pages) Texas Instruments – Low-EMI, High-Performance Four-Channel LED Driver

www.ti.com
7 Detailed Description
LP8861-Q1
SNVSA50A – AUGUST 2015 – REVISED NOVEMBER 2015
7.1 Overview
The LP8861-Q1 is a highly integrated LED driver for automotive infotainment, lighting systems, and medium-
sized LCD backlight applications. It includes a boost/SEPIC converter with an integrated FET, an internal LDO,
and four LED current sinks. A VDDIO/EN pin provides the supply voltage for digital IOs (PWM and SYNC inputs)
and at the same time enables the device.
The switching frequency on the boost/SEPIC regulator is set by a resistor connected to the FSET pin. The
maximum voltage is set by a resistive divider connected to the FB pin. For the best efficiency the voltage is
adapted automatically to the minimum necessary level needed to drive the LED strings. This is done by
monitoring LED output voltage in real time. For EMI reduction and control two optional features are available:
• Spread spectrum, which reduces EMI noise spikes at the switching frequency and its harmonic frequencies.
• Boost/SEPIC can be synchronized to an external clock frequency connected to the SYNC pin.
The four constant current sinks for driving the LEDs provide current up to 100 mA per sink and can be tied
together to get a higher current. Value for the current value is set with a resistor connected to the ISET pin.
Current sinks that are not used must be connected to the ground. Grounded current sinks are disabled and
excluded from the adaptive voltage and open/short LED fault detection loop.
Brightness is controlled with the PWM input. Frequency range for the input PWM is from 100 Hz to 20 kHz. LED
output PWM follows the input PWM so the output frequency is equal to the input frequency.
The LP8861-Q1 has extensive fault detection features:
• Open-string and shorted LED detections
– LED fault detection prevents system overheating in case of open or short in some of the LED strings
• V_IN input-overvoltage protection
– Threshold sensing from VIN pin
• V_IN input undervoltage protection
– Threshold sensing from VIN pin
• V_IN input overcurrent protection
– Threshold sensing across R_ISENSE resistor
• Thermal shutdown in case of die overtemperature
• LED thermal protection with a external NTC (optional feature)
Fault condition is indicated with the FAULT output pin. Additionally, the LP8861-Q1 supports control for an
optional power-line FET allowing further protection in boost/SEPIC overcurrent state by disconnecting the device
from power-line in fault condition. With the power-line FET control it is possible to protect device, boost
components, and LEDs in case of shorted V_BOOST and too-high V_IN voltage. Power-line FET control also features
soft-start which reduces the peak current from the power line during start-up.
Copyright © 2015, Texas Instruments Incorporated
Product Folder Links: LP8861-Q1
Submit Documentation Feedback
11