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Protecting Concerto ADC input / ADCxVREF pins

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

  • 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

  • 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

  • Hi,

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

    Regards,

    Gautam

  • 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?

  • 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