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Protecting Concerto ADC input / ADCxVREF pins

Jo Amer
Prodigy 40 points

Hi,

During power-up of the device the analog input pins (ADC1Ax, ADC1Bx, ADC2Ax, ADC2Bx, ADC1VREFHI, ADC2VREFHI) of the Concerto MCU are powered but the Concerto MCU is not yet powered by 3.3V. (up to 100ms)

How should we deal with this operating case ?

Is there an Application note that describes this situation and how to protect the analog input (ADC1Ax, ADC1Bx, ADC2Ax, ADC2Bx) and the ADCxVREF pins ?

Thanks in advance,


Jo

  • 0
    Guru 192875 points

    Hi Jo,

    Can you elaborate on:

    During power-up of the device the analog input pins (ADC1Ax, ADC1Bx, ADC2Ax, ADC2Bx, ADC1VREFHI, ADC2VREFHI) of the Concerto MCU are powered but the Concerto MCU is not yet powered by 3.3V. (up to 100ms)

    I would like to know, what are the inputs to ADC channels and a brief info about the above statement.

    Regards,

    Gautam

  • 0 in reply to Gautam Iyer
    Prodigy 40 points

    Hi Gautam,

    The analog part of the device, supplied by +/-15V, is powered first. Outputs of Op-amps are connected via resistors and clamping diodes to the Concerto MCU. The two ADCxVREF are powered  by precision voltage regulators.

    With some millisecs delay, the Concerto MCU is powered by the 3.3V powersupply.

    I am looking for an application note that helps to find the right resistors, clamping diodes, capacitors for protecting the inputs of the Concerto MCU ADCs.

    Regards,

                             Jo

  • 0 in reply to Jo Amer
    Guru 192875 points

    Hi,

    There's no application note as such but you can refer schematics of the evaluation boards and kits.

    Regards,

    Gautam

  • 0 in reply to Gautam Iyer
    TI__Guru 60865 points

    Hi Jo,

    Does your +/-15V power supply have a digital disable input? Could you connect this to the reset pin of the MCU to disable the analog section until the MCU comes out of reset?

  • 0 in reply to Devin Cottier
    Prodigy 40 points

    Hi Devin,

    The power supply don't have a disable input.

    Now we power the ADC1VREFHI, ADC2VREFHI inputs of the MCU by voltage regulators supplied by 3.3V.

    We want protect the ADC inputs by resistors (~1kOhm) and clamping diodes (no schottky diodes).

    Which diodes are recommended by TI for protecting the ADC inputs ? Whats about the internal clamping diodes of the concerto MCU if a current of ~15mA flows ?

    Regards,

    Jo