Lx1692 Protection Pin 🎉

Internally, the PROT pin is connected to:

Normal Operation: The pin is pulled high (≈5V) by the internal current source. Fault Condition: The IC turns on the internal open-drain transistor, grounding the PROT pin (≈0V). Latch: Once the PROT pin is pulled low (by internal or external means), the IC latches off all PWM outputs. The only way to restart is to cycle the ( V_CC ) power (power-on reset).

A: This indicates a thermal fault. A capacitor or resistor near the protection pin is heat-sensitive. As the board warms up, the component’s value drifts, raising the protection pin voltage. Use freeze spray to identify the faulty component. lx1692 protection pin

| State | PROT Pin Voltage | IC Outputs (PWM) | |---|---|---| | Normal | ~5V | Switching | | Fault detected (first few cycles) | ~5V (no change) | Switching | | Fault confirmed | 0V | Hi-Z (off) | | After ( V_CC ) reset | ~5V (rising edge) | Switching resumes |

The irony of protection circuits is that they protect the hardware, but they often become the most frequent cause of "black screen" symptoms. Technicians frequently encounter the following scenario: Internally, the PROT pin is connected to:

This is the classic "two-seconds-to-black" syndrome, and the LX1692 protection pin is almost always involved.

The protection pin often reads voltage from a resistive divider connected to the lamp return or the transformer’s secondary. As resistors drift in value (common in older electronics), the voltage on the protection pin can creep up to 1.5V or higher, falsely triggering shutdown. Normal Operation: The pin is pulled high (≈5V)

On the LX1692 datasheet, the protection pin is often labeled as Pin 11 (PRO) or simply the protection input. Its function is binary:

Think of it as the emergency stop button for your screen’s backlight. When any internal or external fault condition occurs—such as a broken CCFL tube, a shorted transformer, or an over-voltage event—the chip pulls the protection pin high (or receives a high signal), and the backlight dies.

Cracks in the solder holding the inverter transformer create intermittent contact. The protection pin sees random spikes and shuts the system down. Fix: Reflow the transformer pins.