• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 3 answers
  • Subscribers 99 subscribers
  • Views 435 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

about the ADC circuitry

user1201164
Expert 1770 points

Part Number: AM4372

HI,.

A customer of ours has asked about the ADC circuitry of the AM4372.
They are looking at Figure 12-4. in TRM.

ADC1_0/2/4/6 are connected to analog voltage input and adc1_1/3/5/7 to GND, but they are concerned about the effect of leakage current at this time.

(1) What is the resistance tolerance of the 9kΩ resistor in the differential line?

(2) The bottom of the figure states "The differential input impedance of each preamplifier is 18 kohms biased to VDDA_ADC1 divided by 2 with a 22k-50k ohm source.
Can I assume that the Bias Supply in Figure 12-4. is a circuit in which VDA_ADC1 is divided by 2 with a 22k-50k resistor?

Best Regards,

Kouji Nishigata

  • 0
    TI__Guru 64655 points

    The primary application expected for ADC1 was a card reader, so the AFE was optimized for this function. Therefore, its implementation is not friendly for a general-purpose ADC application. The resistor tolerance for the internal resistance is not defined, because they were included to bias a card reader head to mid-supply and their absolute value is not important for that application.

    Yes, this statement was simply trying to define the source impedance of the Bias Supply block in this figure.

    I'm not sure what you are trying to measure with ADC1, but its AFE makes it very difficult to use as a general-purpose ADC. Your source impedances will need to be very low to achieve any significant accuracy due to all of the internal biasing.

    Regards,
    Paul

  • 0 in reply to peaves
    Expert 1770 points

    Hi,Paul

    Thanks for your answer.

    However, in chapter 12.1 of the TRM, there is a note that reads

    NOTE: The magnetic card reader function is not supported on the AM437x product family.
    ADC1 should only be used as a general-purpose ADC when using an AM437x device.

    Yet it is difficult to say to a customer, "it very difficult to use as a general-purpose ADC".
    Is it correct to say "High accuracy cannot be expected with ADC1" to the customer?

    Best Regards,

    Kouji Nishigata

  • 0 in reply to user1201164
    TI__Guru 64655 points

    I think you should be honest with the customer and tell them it was not optimized to operate as a general-purpose ADC. Therefore, it may be difficult to achieve the accuracy they need.

    It can be used as a general-purpose ADC but there is a good chance performance will be very limited.

    Regards,
    Paul

  • 0 in reply to peaves
    Expert 1770 points

    Hi,Paul

    Thanks for your reply.

    I was concerned that denying what is written in the TRM would cause a lot of problems.
    I will add to their response that "ADC1 is not optimized to operate as a general-purpose ADC and may have difficulty achieving the required accuracy."

    Best Regards,

    Kouji Nishigata

  • 0 in reply to user1201164
    TI__Intellectual 1590 points

    Hello Kouji Nishigata,

    Thank you for the note.

    Regards,

    Lavanya M R.