Lx1692 Protection Pin 2021

The LX1692 is a widely used third-generation Direct Drive CCFL (Cold Cathode Fluorescent Lamp) controller, primarily found in LCD TV and monitor backlight inverters. A critical component of its operation is the protection system, designed to safeguard the inverter and lamp from electrical faults. Understanding the LX1692 Protection Mechanism

The LX1692 integrates several safety features that monitor the operating conditions of the CCFL lamps and the transformer. When these circuits detect an anomaly, the IC triggers a "protection mode" to shut down the output gate drivers, preventing damage to the external MOSFETs or the high-voltage transformer. Key protection features include:

Open Lamp Protection: Detects if a lamp is disconnected or broken.

Short-Circuit Protection: Shuts down the system if a short is detected in the lamp or secondary transformer winding.

Arc Protection: Triggers if high-voltage arcing occurs, which can be a fire hazard.

Programmable Time-Out Protection: Allows a specific "strike interval" for the lamps to ignite before the IC enters a fault state. The LX1692 Protection Pin

While many backlight ICs have a dedicated pin labeled "PROT" or "TIMER," the LX1692 manages its protection logic through several functional pins. In technical repair communities, identifying the specific pin to modify or monitor is essential for troubleshooting "two seconds to black" issues where the backlight shuts off immediately after powering on. Pin Function Description ENABLE

The primary chip enable input. Logic high enables all functions; logic low disconnects internal power. I_R (Current Ref) lx1692 protection pin

Sets internal bias currents and determines the strike time-out interval. C_BST (Burst Cap) Used for digital dimming and programmable burst frequency. Troubleshooting and Bypassing Protection

In professional repair scenarios, technicians often "bypass" the protection pin to determine if a shutdown is caused by a faulty IC or an actual problem with the lamps/transformer. For the LX1692, bypass methods often involve manipulating the Timing or OLP (Open Lamp Protection) feedback loops. Common Bypass Techniques (For Diagnostic Use Only):

Resistor Grounding: Some variations of this IC series allow bypassing by connecting a resistor (often around

) from the protection-sensing pin to ground to simulate a "normal" load.

LED/Diode Method: Similar to other backlight controllers like the FAN7314, some technicians use an LED or a 1N4148 diode to clamp the protection voltage.

Warning: Bypassing the protection pin should only be done for testing. Running an inverter without active protection can lead to transformer overheating or fire if a genuine short circuit exists. Technical Specifications Summary

For detailed pinouts and electrical characteristics, you can consult the official Microsemi LX1692 Datasheet or Mitsumi Electronics Datasheet. Operating Voltage: 7V to 22V. Package Types: 20-Pin TSSOP and SOIC. Dimming Range: Greater than 60:1 using combined methods. lx1692 PDF | PDF | Electronic Circuits | Capacitor - Scribd The LX1692 is a widely used third-generation Direct

To address your request about the LX1692 protection pin , it is important to understand its role in a CCFL (Cold Cathode Fluorescent Lamp) inverter circuit and how technicians interact with it during repairs. The Role of Protection on the LX1692 Microsemi LX1692

is a resonant full-bridge CCFL controller designed to drive backlight lamps in LCD screens. Its protection circuitry is a safety feature meant to prevent damage from: Open Circuits : If a lamp is broken or disconnected. Short Circuits

: To protect the internal MOSFET drivers and external transformers. Strike Failures

: If the lamp fails to ignite within a set "strike interval". Bypassing Protection (A Common "Story" in Repairs)

In the world of TV and monitor repair, a "helpful story" often involves disabling this protection to diagnose whether a shutdown is caused by a faulty lamp or a sensitive controller. For the

(and its close relatives like the MSC1692), technicians often use a to bypass this safety trip. Common Method : For many controllers in this family, connecting a 220kΩ resistor

from the protection-related pin (often Pin 4 or Pin 14, depending on the specific board layout) to Ground (GND) can "trick" the chip into staying on. Alternative : In some variations, technicians use a Common Faults That Trigger the LX1692 Protection Pin

connected to the protection pin to maintain a specific voltage level that prevents the shutdown trigger. Key Technical Details According to technical documentation for the Strike Interval

: The time the chip waits for a lamp to start is determined by external resistors (RI_R) and capacitors (CC_TO). Enable Pin Enable Input

(typically Pin 1 or similar) must be high (>1.85V) for the chip to function at all. : Disabling protection is

. It can cause high-voltage transformers to overheat or catch fire if a genuine short circuit exists. It should only be done briefly for testing, not as a permanent fix. Troubleshooting Steps

If your LX1692-based backlight is turning on and then immediately off: Check Transformers

: Measure the resistance of the secondary windings; they should be nearly identical (typically around 1kΩ). Inspect Lamps

Common Faults That Trigger the LX1692 Protection Pin

Understanding what should trigger the pin helps you know when not to bypass it.

LX1692 Protection Pin — Overview and Guidance

Q: My monitor has no backlight at all, not even a flash. Is it the protection pin?

A: No. If there is no flash, the LX1692 is not even trying to start. Check the Vcc supply pin (typically Pin 2) for 5V to 24V. Also check the enable pin (Pin 1). No enable signal = no oscillation = protection pin irrelevant.

PCB/layout guidelines

  • Short, direct trace from LX1692 pin to pull-up and MCU; avoid routing near high-current traces.
  • Place pull-up and series resistor close to the LX1692.
  • Keep analog grounds and sensing traces separate from power ground; use single-point star connection.

Electrical characteristics (typical/spec example)

  • Output type: Open-drain NMOS (pulls to GND when active)
  • Active level: Low (asserted = 0V)
  • Maximum sink current: 10 mA (to drive LED or MCU input)
  • Off-state leakage: < 1 µA
  • Pull-up voltage: 1.8–5.5 V tolerated (external pull-up required)
  • Propagation delay: < 50 µs from fault detection to pin assertion
  • Debounce/hysteresis: 2–10 ms internal configurable
  • Reset input threshold (if integrated): CMOS logic levels (Vih ~ 0.7Vdd, Vil ~ 0.3Vdd)

Q: Is the LX1692 still in production?

A: Microsemi (now Microchip) produced the LX1692. For new designs, it is considered obsolete, but large quantities exist on the secondary market (eBay, Aliexpress, UTSource).