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OPA2197: Thanks for kindly help

LI Iwan
Intellectual 270 points
Part Number: OPA2197


一、Customer's FTU products，Acquisition of zero sequence voltage  by electronic transformer，Load impedance requirement is greater than 5M:

二、Customers's’current circuit ,for system test,the input of AI15 = 6.5*1.2*1.414V,and the output AC0 ≈11.0V。More than the input of ADS8688S。

三、Please help to assess whether the following corrective measures are correct：

1、The output of the electronic transformer is divided by two 2.5M resistors in series and then input  the ADC8688S.

2、The output of the VAC0 is divided by two 2.5M resistors in series and then input  the ADC8688S.

3、If the signal is reduced directly by the amp(FU13A), it will affect the input impedance of the amplifier or not.(Demand is greater than 5M).

Thanks for kindly help.

  • 0
    TI__Guru* 93105 points
    Hi LI,

    Is the issue the transformer cannot be loaded by a resistance lower than 5 Megohms? If the voltage divider is added after the op amp, then it will not load the transformer. Note that the input impedance of a SAR converter is dynamic and changes at different points in the conversion cycle. SARs often require careful selection of both the op amp that will drive them and the RC components connected between them.

    Regards, Thomas
    Precision Amplifiers Applications Engineering