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LM98640 input signal range

chirag prajapati
Prodigy 20 points

Sir

We plan to use LM98640 to process Infra-Red detector output which is 2V range with 2V of fixed offset. Fixed offset of 2V needs to be subtracted from signal. We plan to do it externally using OSx+ and OS- pins. If you refer Figure 10 on page 26 of datasheet, Csh capacitor can remove fixed offset voltage. Please, tell me can 98640 input take 4V maximum when other input is at 2V fixed level ? After differential input going to capacitor, fixed voltage will get cancelled out. In this case, can input be more than 2.85V specified in datasheet ? What is CMRR of first stage ? We need 14 bits digitization to cover large dynamic range of infra-red camera. Please, reply.

  • 0
    TI__Genius 17125 points

    Please see the abs max table in the datasheet.   The abs max on the input is 0.3V above the supply voltage.  4V will violate the abs max and could damage the par or at least impact the lifetime of the device.

    Exceding the 2.85V inut range will impact the accuracy of the measurements.   The input range should be centered on the supply rails for best performance.