Checking Open LED Protection in a Boost Backlight Driver

A boost LED driver normally raises its output until the commanded LED current flows. If the string opens, that current cannot be established, so the normal regulation objective is no longer reachable. Check the protection response before relying on the voltage measured with a healthy LED string.

Identify the protection mechanism

Read how the selected driver detects an open load or excessive output voltage and what action follows. The TI TPS61169 documentation describes integrated open LED protection that disables the converter to limit output voltage during an open LED condition. Other devices may latch, retry, or report the event differently.

Record the relevant thresholds, tolerances, and component ratings from the current data sheet. Distinguish a protection threshold from an absolute maximum rating; they serve different purposes.

Review the entire output path

Include output capacitor, rectifier, switch node components, connector, and any downstream protection. Determine which nodes rise when the current path opens. A component outside the driver’s package can reach an unacceptable voltage even if the controller itself survives.

Consider where the opening occurs. Disconnecting the complete load at a connector may not produce exactly the same node conditions as one LED opening inside a string. Choose tests that represent the faults relevant to the product.

Measure the event with a controlled setup

Use a suitable method to introduce the open condition within the circuit’s reviewed energy and voltage envelope. Capture output voltage, switching behavior, input current, and any fault indication. Include the peak and the subsequent steady or retry behavior.

Do not rely solely on a slow voltage reading. A brief overshoot or repeated charge cycle can be missed by a display that shows only the average output voltage.

Verify reconnection and restart

Check the documented recovery sequence and the effect of restoring the LED path. Determine whether the output capacitor remains charged and whether reconnection creates a current pulse outside normal regulation. Use the manufacturer’s supported restart method.

Save fault location, input condition, protection waveform, peak voltage, and recovery result. Repeat where required at the highest relevant input and LED configuration. A satisfactory result establishes that the open load response respects the reviewed component limits and returns to a defined state. The presence of a feature named open LED protection does not replace verification of the complete board, its stored energy, and its behavior when the string is connected again. Record whether the test begins from an illuminated or disabled state.