To understand the gravity of the protection pin update, one must first understand the inherent fragility of LED backlight systems. In the era of the original MP3378, the primary nemesis was the "Open Circuit." When a string of LEDs disconnects, the driver attempts to push current into a void. Without intervention, the boost converter increases its output voltage to the breaking point, risking damage to the MOSFET, the diode, and the insulation of the PCB traces.
Designers must confirm whether the PROT pin is active-high or active-low and whether it sources or sinks current. mp3378e protection pin upd
Because a boost converter inherently generates high voltages that can exceed safe thresholds if left unregulated, the IC integrates multi-tiered fault detection directly into its key control pins. Key Protection Pins and Diagnostic Behaviors To understand the gravity of the protection pin
| 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 | Designers must confirm whether the PROT pin is