: The failed, dim, or shorted string will display a highly unstable current waveform, pinpointing exactly which row of backlights within the LCD panel requires physical replacement. ⚙️ Safe and Permanent Repair Best Practices
By understanding the voltage thresholds, timing windows, and external component interactions that lead to UPD, you can quickly resolve “dead backlight” faults and design more robust LED drivers. The key takeaway:
[Power On Display] │ ▼ Does the backlight flash briefly? ├── NO --> Check VIN (Pins 13/15), EN1 (Pin 14), and VCC1 LDO output. └── YES --> IC is entering Protection Mode. Proceed below. │ ▼ Measure voltage at Pin 9 (OVP) during the brief flash: ├── Voltage exceeds threshold --> Check for an open LED string or damaged feedback resistors. └── Voltage remains low --> Check for shorted LEDs or a faulty external boost MOSFET. 1. Identifying Open LED Strings
If you are working on a specific repair, what are the symptoms you are seeing? Is it no backlight or flashing backlight? If you want, I can: Give you specific pin voltages for troubleshooting Suggest methods to bypass the OVP pin for testing MP3378 - micrIC mp3378e protection pin upd
This is not merely a story of a pin; it is a story of the transition from passive anxiety to active guardianship.
Sets the current for each LED string via an external resistor.
To help narrow this down, feel free to share when it turns on, or if the buck converter side is still outputting power after the backlight cuts off. Share public link : The failed, dim, or shorted string will
RDS(ON)cap R sub cap D cap S open paren cap O cap N close paren end-sub
Instead of permanently bypassing protections, follow this bench workflow to safely isolate the defect: Expected Metric / Outcome Check Inputs VIN1cap V cap I cap N sub 1 VIN2cap V cap I cap N sub 2 receive stable 12V or 24V power rails. 2 Monitor EN Signals EN1cap E cap N sub 1
Understanding that the shuts down for a reason is key to fixing it. The protection circuitry is robust, designed to keep the panel safe, but it can be sensitive to aging LED backlight strips. ├── NO --> Check VIN (Pins 13/15), EN1
✅ Use (PRO high) for systems where temporary faults shouldn’t require power cycling. ⚠️ Latch-off is safer for permanent faults but requires user reset.
The step-up WLED driver regulates current across four separate LED strings. It controls an external MOSFET to boost the main DC input voltage ( VIN1cap V cap I cap N sub 1
The most stable way to bypass false-positive protection triggers without damaging the IC is to artificially clamp the OVP pin feedback loop. MP3378E - Monolithic Power Systems
Detects failures in individual LED strings and reacts accordingly. Thermal Protection: Recoverable Thermal Shutdown Over-Temperature Protection (OTP) for the whole IC. Hardware Protection:
Monitors current through the external switching MOSFET via a sense resistor to catch short circuits.