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UCC27201A: Applying external test voltage to 'gate' pins while powered down

Part Number: UCC27201A

Hello,

I'd like to understand if there are any immediate, and/or long-term reliability issues with applying a test voltage to HO/HS/LO pins while the device/board is powered down.

Reason: I'd like to apply a test voltage to the gates of the FETs to ensure FET is functioning correctly.

Is this possible, any limitations?

Thank you in advance,

Iain

  • Hello Lain,

    Depending on the voltage you want to apply, to which pins there may be a concern. If you apply voltage to the LO pin, there is a path thru the driver internal FET (body diode) which will source current into the VDD pin. When the VDD pin is ~1.5V the driver will turn on the driver output pull down and try to clamp the LO voltage low. The HO pin has a similar behavior with sourcing current into the HB pin. If DC voltage is applied to the driver outputs, the driver will try to clamp the outputs low and likely have excessive power dissipation.

    Regards,

  • Hello Richard,

    Thank you for your response, I appreciate the insight. This does help further my understanding.

    I've attached a connection diagram; would this change or add anything further to your response (specifically the HO/HS connectivity)?

    Thank you in advance,

    Iain

  • Hello Lain,

    With 15V applied to the driver outputs, the VDD will be biased up by LO and HB-HS will be biased up by HO. When VDD or HB is ~1.5 to 2V the diver pull down device will be turned on and will clamp the driver output. You really cant apply this voltage to the driver outputs without the driver trying to clamp this voltage so you would not be able to turn on the external Mosfets.

    Any reason VDD cannot be provided and turn on the driver outputs to check the Mosfets?

    Regards,

  • Richard,

    Dually noted. I appreciate you driving this towards a conclusion. 

    Unfortunately, the upstream controller would also give similar issues, so powering VDD and using inputs isn't an option either.

    Thank you for the assistance,

    Iain