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TMS320F28034 VDDA, VDDIO, VDD power down while VREFHI is existing

Toshio Ushikubo
Mastermind 9620 points
Other Parts Discussed in Thread: TMS320F28034

Hello,

Please answer following question from Customer.

Customer is using TMS320F28034 for their trial board and using external reference for ADC.

Please advise if F28034 will damage in case of following condition.

3.3V is applied to VREFHI and VDDA, VDDIO and VDD are power-down.

(Customer measured current and 36mA is flowing into VREFHI terminal.)

Best Regards.

  • 0
    TI__Expert 7885 points
    Hello Toshio,

    Yes. This is not recommended. We are adding the following text to the datasheet (Power Sequencing section 5.11):

    "No voltage larger than a diode drop (0.7 V) above VDDIO should be applied to any digital pin *(for analog pins, this value is 0.7 V above VDDA)* prior to powering up the device. Voltages applied to pins on an unpowered device can bias internal p-n junctions in unintended ways and produce unpredictable results."

    Best Regards,
    Adam Dunhoft
  • 0 in reply to Adam Dunhoft
    Mastermind 9620 points

    Hello Adam-san,

     

    Thank you for your answer.

     

    Could you please answer following additional request.

    Customer did the test to leave F28034 VDDA=0V and VREFHI=3V during 2 hour in 125C environment, but F28034 seems work normally.

     

    Could you give us internal circuit drawing related to VDDA<VREFHI issue to explain the expectable internal damage.

     

    Best Regards.

  • 0 in reply to Toshio Ushikubo
    Mastermind 9620 points
    Hello Adam-san,

    Please respond for my request.

    Best Regards.
  • 0 in reply to Toshio Ushikubo
    TI__Expert 7885 points
    Hello Toshio,

    Sorry, I do not have an internal schematic to share. It is not surprising that the customer sees the device working normally, but that is not something that can be guaranteed as there is no fail-safe mechanism for the VREFHI pin. Driving this pin while not powering the circuit with a proper VDDA voltage could result in damage to the device.

    Best Regards,
    Adam Dunhoft