We’re currently facing an issue with the L4986A PFC controller in one of our designs. The IC is not functioning as expected, and we would appreciate your guidance.
:wrench: Issue Summary:
• The IC receives all input voltages within the recommended operating range.
• However, Pin 8 (COMP) is consistently outputting 10V, regardless of load or feedback conditions.
• No switching activity is observed at the gate driver output (GD), and the PFC stage remains inactive.
:pushpin: Troubleshooting Done:
• Verified VCC, CS, FB, and PG_IN voltages are within spec.
• Checked for shorts or open connections around COMP pin circuitry.
• Replaced the IC with a fresh unit—same behavior persists.
• Load and input conditions are stable and within design limits.
:paperclip: Design Context:
• Application: Bridgeless CCM PFC stage for 350W SMPS
• Based on ST’s reference design EVL4986-350W
• COMP pin connected to standard RC compensation network as per datasheet
:question_mark:Request for Support:
• What conditions could cause COMP to saturate at 10V?
• Could this indicate a fault in the internal error amplifier or feedback loop?
• Are there known failure modes or startup lockouts that could explain this behavior?
We’d be grateful for any insights, debug suggestions, or reference schematics that could help us resolve this issue. If needed, we can share scope captures and layout snippets.
Thank you in advance for your support.
