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LM25066I-EVM: LM25066: Random Circuit Breaker Fault & IIN_OC Fault — MOSFET Gate Stuck at ~0.7 V

ADARSHA A N
Intellectual 255 points

Part Number: LM25066I-EVM
Other Parts Discussed in Thread: LM25066

Hello Team,

Please find the attached schematic.PVT_LM25066.pdf

We are using the LM25066 as a 12 V supply current limiter for a GPU in one of our products, which is currently in mass production. Recently, we have encountered an issue where the output does not power up on some boards. This issue has appeared on more than four units so far.

When we read the PMBus status registers, we observed the following:

  • STATUS_INPUT (Reg: 0x7C), Bit 2 = 1 → IIN_OC Fault

  • STATUS_MFR_SPECIFIC (Reg: 0x80), Bit 7 = 1 → Circuit Breaker Fault

  • STATUS_WORD (Reg: 0x79), Bit 6 = 1 → MOSFET not switched ON

These bits indicate that the device is preventing the MOSFET from turning ON due to an over-current or protection condition.We also probed the MOSFET gate voltage during the fault and observed it is approximately 0.7 V (never goes high), confirming that the LM25066 is holding the gate OFF. 

We are not seeing this behavior across all boards, but it has started appearing randomly.

Request for Assistance

  1. Could you please help us understand what conditions may trigger this combination of faults?

  2. Has TI received any similar reports from other customers using LM25066?

  3. Are there any recommended checks for debugging this issue on hardware?

  4. Under what conditions would the circuit breaker fault occur even if the actual load startup current is within the design limit?

Any insights will be very helpful.
Thank you in advance.