is a integrated circuit from Monolithic Power Systems (MPS) designed for monitor applications. It combines a 4-string WLED controller for backlighting with a high-efficiency buck converter for internal power. MPS | Monolithic Power Systems The "protection pin" functionality primarily relates to the OVP (Over-Voltage Protection)
: Includes recoverable thermal shutdown, meaning the device will restart once it cools to a safe operating temperature. External Control MP3378E datasheet
MP3378E Protection Pin UPD: Deep Dive Guide to Over-Voltage Protection (OVP) and Backlight Diagnostics
When troubleshooting backlights managed by MPS controllers , technicians modify the feedback pins to stop the IC from shutting down. This allows them to measure the operating currents across all four channels and find the fault. mp3378e protection pin upd
| Protection Type | Detection Method | Fault Response & Thresholds | Critical Pins | | :--- | :--- | :--- | :--- | | | Monitors the boosted output voltage | Event : Output exceeds programmable OVP threshold set by resistor divider on OVP pin. Response : Controller stops switching and latches off until reset. Trigger after fault persists for 4μs. Benefits : Prevents damage to LED strings and external MOSFET from excessive voltage. | OVP, VOUT | | Under-Voltage Protection (UVP) | Monitors VIN1 and VCC1 internal regulator | Event : Input voltage or internal 6V regulator drops below threshold. Response : Entire WLED controller shuts down until voltage recovers. Benefits : Prevents erratic operation from insufficient supply voltage. | VIN1, VCC1 | | Over-Current Protection (OCP) | Senses current via external sense resistor (R_SENSE) on ISENSE pin | Event : Inductor current exceeds current limit. Response : Stops switching; after 512 switching cycles of clamped COMP voltage, controller turns off and latches. Benefits : Protects external MOSFET and inductor from excessive currents. | ISENSE, COMP, GATE | | Over-Temperature Protection (OTP) | Monitors silicon die temperature via internal sensor | Event : Junction temperature > 150°C (typical). Response : Controller shuts down when exceeding upper threshold; returns to normal operation when temperature drops below lower threshold (recoverable). Hysteresis ~ 20°C. Benefits : Prevents thermal damage under high ambient temperature or heavy load conditions. | Internal | | LED Open-String Protection | Monitors LEDX (pin 14, 13, 12, 11) voltages per string | Event : Any string voltage below 190mV indicates open LED string. Response : Controller marks off faulty string; remaining strings regulate normally. If all strings open, controller shuts down until reset. Benefits : Allows continuous backlighting with remaining strings while protecting against open-circuit failures. | LED1, LED2, LED3, LED4 | | LED Short-String Protection | Monitors LEDX voltage exceeding 6.3V | Event : LEDX voltage > 6.3V for 4096 switching cycles. Response : Fault string marked off and disabled; disconnected from output voltage loop. Marked strings shut off completely until boost part restarts. Note : Protection disabled when all used channels have VLEDX > 1.5V to prevent mistriggering. | LED1, LED2, LED3, LED4, ADIM | | Inductor/Diode Short Protection | Dual detection: COMP voltage clamping and MOSFET current sensing | Method 1 : COMP voltage clamped high for 512 switching cycles. Method 2 : Current sense voltage across R_SENSE hits VLMT limit for 4 switching cycles. Response : Controller turns off and latches in both cases. Benefits : Critical for preventing catastrophic damage when external inductor or diode fails short. | COMP, ISENSE, GATE | | Bootstrap UVLO Protection | Monitors BST-SW voltage differential for floating driver | Event : BST-SW voltage < 2.2V. Response : Disables high-side MOSFET driver, preventing shoot-through. Typical hysteresis of 150mV. Benefits : Ensures sufficient gate drive voltage for external power MOSFET. | BST, SW |
For repair technicians, hardware engineers, and electronics enthusiasts, understanding the mechanisms is essential. Hardware failures often cause the IC's stringent safety logic to trigger a latch-off state, causing the common "screen flashes then goes black" symptom. Technical Architecture of the MP3378E
The MP3378E doesn't have a single "protection pin." Instead, it uses a network of monitoring pins to trigger a shutdown if any safety threshold is exceeded. Understanding these pins is the key to diagnosing a backlight that flashes then dies. MP3378E - Monolithic Power Systems is a integrated circuit from Monolithic Power Systems
Bypassing protection mechanisms is strictly an emergency diagnostic protocol or a temporary troubleshooting measure. Leaving protection permanently disabled removes vital safeguards, which can cause severe thermal damage, short circuits, or display fires. Why Technicians Modify the Protection Circuit
: Using external resistors or pins to set a delay before a permanent shutdown occurs. This prevents nuisance tripping from transient voltage spikes while still protecting against sustained shorts. Standby Bus Stability
: If an LED string is open or shorted, avoid replacing a single diode. The remaining aged diodes will soon experience over-current stress and fail. Replace all internal strips with new, high-quality replacements. Response : Controller stops switching and latches off
High-speed switching can cause "false" protection triggers. It is recommended to route the signal to the protection pins through a low-pass RC filter (e.g., resistor and 10nF10 n cap F capacitor) to suppress switching noise.
Inputs for the four LED strings, which can handle voltages up to Protection Pin Update (Deprotection)
Detects failures in individual LED strings and reacts accordingly. Thermal Protection: Recoverable Thermal Shutdown Over-Temperature Protection (OTP) for the whole IC. Hardware Protection:
The MP3378E features a sophisticated protection architecture designed for high-reliability monitor applications. Unlike simpler drivers, it provides independent protection for both the WLED step-up controller and the buck converter. 1. Programmable Over-Voltage Protection (OVP)