The source current of the external boost power MOSFET flows through a current-sense resistor hooked up to the . MP3378E - Monolithic Power Systems
The MP3378E is housed in a compact (Exposed Pad) package. While it controls both a buck regulator and a boost backlight driver, its diagnostic loops are centered on a few critical pins:
Previous iterations suffered from "nuisance tripping." A sudden inrush of current or a momentary electrostatic discharge could trigger the protection pin, shutting down the display unnecessarily. The updated protection logic in the MP3378E variant introduces tighter hysteresis. It allows the pin to "hold" its state during minor fluctuations, ensuring that the protection mechanism acts as a filter, not just a switch. It whispers "wait" before it screams "stop." mp3378e protection pin upd
The MP3378E integrates a step-down converter to create an internal bus voltage (e.g., 3.3V or 5V). This converter has its own set of protections.
When an LED fails in the middle of a movie, and the screen dims slightly but does not turn off, they are witnessing the work of this updated protection logic. When a vehicle’s dashboard survives a voltage spike from a starter motor, it is this pin that held its ground. The source current of the external boost power
VLEDX_OVcap V sub cap L cap E cap D cap X _ cap O cap V end-sub VLMTcap V sub cap L cap M cap T end-sub Thermal Shutdown TSTcap T sub cap S cap T end-sub Design Updates and Best Practices (The "UPD")
Enters Hiccup Mode to limit power dissipation during direct electrical shorts. Internal Die Sensor The updated protection logic in the MP3378E variant
If an LED string becomes open-circuit, the output voltage will rise; the OVP pin detects this spike and shuts down the external MOSFET to prevent component failure.
In the television and monitor repair industry, a common diagnostic symptom is . This indicates that the MP3378E successfully completes its initial soft-start sequence, detects a faulty string or a mismatch via the VLED pins, updates the fault latch, and cuts power to the inverter circuit to prevent damage. Verifying Protection vs. Hardware Failure
The MP3378E is a step-up (boost) controller IC designed for large-size LCD panel backlighting (TVs, monitors). Unlike typical boost controllers, it features a multi-function that serves as both an Over-Voltage Protection (OVP) input and a Start-Up timing capacitor node.
The MP3378E has an established reputation in the repair community, particularly as a common failure point in LG monitors. A classic sign of a failed MP3378E is a monitor that goes completely dark (no backlight) while the power LED remains lit. The root cause is often an internal short on the chip's 12V supply rail. This is confirmed by online discussion where technicians have found of the MP3378E is shorted to ground, which carries the 12V supply voltage for the internal buck converter.