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ADS7038-Q1: Inquiry of input impendence of ADS7038-Q1 AIN pin

Part Number: ADS7038-Q1
Other Parts Discussed in Thread: ADS1018-Q1, ADS7038

Hi Expert,

The customer is asking the impendence of ADS7038-Q1 AIN pin.And they found the ADS1018-Q1 had defined this into datasheet.

Pls advice.

Best regards,

Eric Lai

  

Field Application Engineer

Texas Instruments Taiwan Limited

O: +886-2-2175-2582

M: +886-909-262-582

E-Mail:Eric.Lai@ti.com         

  • Hello,

    The ADS7038-Q1 is a SAR device, while the ADS1018-Q1 is a delta sigma, this are inherently different and thus the input impedance is not specified in one vs the other. 

    The ADS7038 -Q1 samples the the input through a switching capacitor circuit, thus the impedance is dynamic, you will not see the input impedance specified in a SAR device for this reason.

    The below image shows what the analog input circuitry looks like. with Rse typically 150 ohm, Csh typically 12pF

    To properly drive the input, you will need to make sure that the Csh is fully charged and settled within the acquisition time (this is based on the sampling rate being used)

    Regards

    Cynthia