Minimum

headroom

level

reached

Open LED

fault

Shorted

LED fault

LOW_COMP

MID_COMP

HIGH_COMP

No actions

No actions

DC-DC

increases

voltage

Open LED fault when

Shorted LED fault (one

output should be

between LOW_COMP

and MID_COMP)

Both outputs are

above headroom

window

DC-DC

decreases

voltage

HEADROOM

WINDOW

HIGH_COMP

MID_COMP

LOW_COMP

OUT#

CURRENT/PWM

CONTROL

LOWEST VOLTAGE

SHORT STRING

DETECTION LEVEL

VOLTAGE THRESHOLD

LP8862-Q1

www.ti.com

SNVSA75A – NOVEMBER 2015 – REVISED NOVEMBER 2015

Figure 9. Comparators for Adaptive Voltage Control and LED Fault Detection

Figure 10 illustrates different cases which cause DC-DC voltage increase, decrease, or generate faults. In

normal operation, voltage at the OUT1 and OUT2 pins is between LOW_COMP and MID_COMP levels, and

When voltage at OUT1 and OUT2 pin increases above MID_COMP level, DC-DC voltage adapts downwards.

When voltage at OUT1 or OUT2 pin falls below LOW_COMP threshold, DC-DC voltage adapts upwards. In the

open LED fault is detected.

HIGH_COMP level, 6 V typical, is the threshold for shorted LED detection. When the voltage of OUT1 or OUT2

pin increases above HIGH_COMP level and the other output is within the normal headroom window, shorted

LED fault is detected.

Figure 10. DC-DC Adaptation and LED Fault Detection Algorithms

Copyright © 2015, Texas Instruments Incorporated

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