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TLV2556 input impedance

Timothy Starr
Expert 2445 points
Other Parts Discussed in Thread: TLV2556

I am looking for a graph of TLV2556 input impedance over temperature. Also what is the recommended drive circuit for this device? Does TI have a recommended R & C flywheel filter?

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    TI__Guru**** 172816 points

    Hi Tim,

    We do not have a graph relating the input impedance of the TLV2556 over temperature.  The switch resistance (worst case) is 600 ohms with a 55pF sample/hold capacitor and the acquisition time is based on how the device is configured (8, 12 or 16 SCLKs).  Going with 15MHz clock and 8 cycle sampling, you have ~533nS acquisition time.  You'll be looking at an amplifier with ~11MHz GBW.  As a starting point for R and C, you might consider ~56ohms and 1.1nF.  The following documents should help you out in trying to find the optimal solution:

    “Designing SAR ADC Drive Circuitry, Part I: A Detailed Look at SAR ADC Operation,” Analog Zone, 2005.
    “Designing SAR ADC Drive Circuitry, Part II: Input Behavior of SAR ADCs,” Analog Zone, 2005.
    “Designing SAR ADC Drive Circuitry, Part III: Designing The Optimal Input Drive Circuit For SAR ADCs,” Analog Zone, 2007.