Time

Driver

headroom

LP8545

www.ti.com

SNVS635D – APRIL 2010 – REVISED DECEMBER 2013

VBOOST[4:0]

Voltage (typical)

00100

4

14

...

...

...

11101

29

39

11110

30

40

11111

31

40

If resistor divider is used for the FB pin to get higher output voltage with external FET, the boost output voltages

are scaled accordingly.

Adaptive Boost Control

Adaptive boost control function adjusts the boost output voltage to the minimum sufficient voltage for proper LED

accordingly. Driver headroom can be adjusted with <DRIVER_HEADR[2:0]> EEPROM bits from ~300 mV to

1200 mV. Boost adaptive control voltage step size is 125 mV. Boost adaptive control operates similarly with and

without PSPWM.

Figure 17. Boost Adaptive Control Principle with PSPWM

Fault Detection

LP8545 has fault detection for LED fault, low-battery voltage, over-current and thermal shutdown. The open drain

output pin (FAULT) can be used to indicate occurred fault. The cause for the fault can be read from status

register. Reading the fault register will also reset the fault. Setting the EN pin low will also reset the faults, even if

an external 5V line is used to power VLDO pin.

LED Fault Detection

With LED fault detection, the voltages across the LED drivers are constantly monitored. LED fault detection is

enabled with <EN_LED_FAULT> EEPROM bit. Shorted or open LED string is detected.

If LED fault is detected:

•

The corresponding LED string is taken out of boost adaptive control loop;

•

Fault bits are set in the fault register to identify whether the fault has been open/short and how many strings

are faulty; and

•

Fault open-drain pin is pulled down.

LED fault sensitivity can be adjusted with <LED_FAULT_THR[1:0]> EEPROM bits which sets the allowable

variation between LED output voltage from 2.3V to 5.3V. Depending on application and how much variation there

can be in normal operation between LED string forward voltages this setting can be adjusted.

Fault is cleared by setting EN pin low or by reading the fault register.

Copyright © 2010–2013, Texas Instruments Incorporated

Submit Documentation Feedback

21

Product Folder Links: LP8545