LM3432, LM3432B

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SNVS498D – APRIL 2007 – REVISED MAY 2013

DYNAMIC HEADROOM CONTROL

To use the DHC function, connect a gain setting resistor from the VDHC pin of the LM3432/LM3432B to the

VDHC pin of the LM3430 (Texas Instruments Semiconductor’s Boost Controller for LED Backlighting) that is

supplying power to the LED rails. The LM3432/LM3432B’s DHC function will regulate the voltage between the

IOUT pins and ground to a minimum of 0.625V typical (IOUT = 20 mA) to optimize overall efficiency. A large

DHC time constant needs to be set in order not to interfere with the loop response of the DC-DC converter. This

can be implemented by connecting a capacitor from the LM3432/LM3432B’s CDHC pin to ground. If the DHC

function is not needed, leave the VDHC pin floating. When operated in this manner, if the lowest voltage between

any of the IOUT pins and ground is greater than 2V, the LED short fault detection function will be disabled. For

the LM3432B, if any open condition occurs on any channels, the DHC function will be inactive and the LED

supply rail voltage from the LM3430 will stay at its preset level. If the excess headroom voltage is greater than

the short fault detect threshold, 7.3V(min), the device may latch off the LED string(s) due to short fault protection.

In order to insure the proper operation of good LED strings, designers must design for sufficient excess

headroom voltage below the short fault detect threshold.

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Product Folder Links: LM3432 LM3432B