UCC28070: About abnormal behavior by AC line voltage drops

Hi Team,

Our customer is evaluating their board.

If heavy output current occurs, FET is stopped.

Therefore, they investigate this cause.

[Investigation content]

If heavy output current occurs, AC input voltage drops by Resistance component of AC line on their board.

And, when VINAC reached around 1.0V(Level1 Threshold) by AC input voltage drops, FET is stopped (they guess that UCC28070s Gate driver is stopped).

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We have three questions.

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[Q1]

If AC input voltage extremely(or unintentionally) descends, does UCC28070 operate abnormally?

(For example, “Gate driver is stopped”, “VCCs UVLO works” etc.)

[Q2]

If VINAC pin voltage extremely(or unintentionally) descends, does UCC28070 operate abnormally (Gate driver is stopped etc.)?

I understand that A change of QVFF levels does not have the problem.

However, could you please let us know if you have other concern?

https://e2e.ti.com/support/power-management/f/196/t/898849?tisearch=e2e-sitesearch&keymatch=About%20QVFF%20levels(circuit)

[Q3]

If AC input voltage extremely(or unintentionally) descends, does UCC28070 affect VCC pin?

(For example, “Current flows from AC line(or other) into VCC pin” etc.)

We evaluated UCC28070EVM.

Then, I let input AC voltage line descend intentionally by addition of the unnecessary resistance.

As a result, DC power supply is stopped.

We guess that “Current flows from AC line(or other) into VCC pin”.

Could you please let us know if you have any answer?

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Regards,

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