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TMDXIDK437X: ADC range

R2d2
Expert 1130 points

Part Number: TMDXIDK437X

Hi,

I would like to confirm my calculation of the adc range.

what is the range of the adc in the idk am437x? is it 0-3.3 ? other ?

what is the value in volts I expect to see when nothing is connected ? is it 1.65 ? other ?

what is the total volts to amperes converstion factor in the board  (max current it can sample) ?

Thanks 

  • 0
    TI__Guru**** 393215 points

    Hi,

    R2d2 said:
    what is the range of the adc in the idk am437x? is it 0-3.3 ? other ?

    AM437x ADC input range is specified in Table 5-5 in the AM437x Datasheet Rev. E.

    R2d2 said:
    what is the value in volts I expect to see when nothing is connected ? is it 1.65 ? other ?

    There is no meaningful value from an unconnected ADC input.

    R2d2 said:
    what is the total volts to amperes converstion factor in the board  (max current it can sample) ?

    The ADC measures input voltages. If you want to measure current you must externally convert it to a voltage within the range specified in Table 5-5.

  • 0 in reply to Biser Gatchev-XID
    Expert 1130 points

    Thanks for taking the time to answer me, but this does not answer my questions.

    I am not asking in general about the sitara am437x. In general

    I am asking about the am437x with respect to the idk schematics

  • 0 in reply to R2d2
    TI__Guru**** 393215 points

    On the IDK both ADC0 and ADC1 are connected to the motor control circuitry. See page 15 of the schematics. You will notice that all inputs connected to voltage sources higher than +1.8V have voltage dividers.

  • 0 in reply to Biser Gatchev-XID
    Expert 1130 points

    thanks

    if I calculate correctly , zero current will read 1.65 V.  Am I correct ?

    since adc range is 0 - 1.8 , this means that the current measurement dynamic range is not symmetric around zero , such that on one polarity we have 0.15 V and on the other we have 1.65V

    Do you know why the current sensing was build around 1.65 and not 0.9 ? is this something to consider in a future design ? or was it done to save the money and PCB place for the additional 0.9 voltage on the circuit ?