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ADS7952: Current Draw on Input Channels

ReedKacz
Intellectual 2540 points
Part Number: ADS7952

Hi ADC Experts!

My customer is running into challenges that the input channels to the ADS7952 are seeing a voltage drop compared to the expected divided down voltage. 

How much current do we expect to see drawn into the ADS7952 inputs when the input is switched on? 

Setup:

VBD=VA=3.3V

CH7 connected to 5V with 30.1kohm and 20kohm divider

VREF = 2.5V

No PGA connected between MX0 and AINP.

Thanks!
Reed

  • 0
    TI__Mastermind 24940 points

    Hi Reed,

    The current consumption is dynamic based on the sampling rate.

    What is the sampling the device is being used at?

    If only channel 7 is having the voltage dip issue, I would first suggest adding a capacitor about 150 pf to 300pf (Csh *10 to 20) in parallel with the second voltage divider resistor. Depending on how fast the device is switching through devices, this cap will already be charged up by the time it is sampled and can help supply the sample and hold circuit of the ADC.

    If this is seen through out all channels, then a buffer at the MXO pin would be a good idea. This might be a good implementation in general.

    If all else fails then decreasing the resistors should help.

    Regards

    Cynthia

  • 0 in reply to Cynthia
    TI__Intellectual 2540 points

    Hi Cynthia,

    Thank you for the quick response! The current draw appears to be on each channel on the order of 8 to 10 micro-amps. I will populate a 150 to 300pF capacitor and install the buffer at MXO.

    Thanks again,

    Reed