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TIPD164: Design Optimization Query

Narashiman P
Prodigy 15 points
Part Number: TIPD164
Other Parts Discussed in Thread: INA826, ADS1248, , INA159, INA823

In TIPD164 design, they have used INA826 and  INA159 for converting voltage and current source to required range for ADS1248 IC . Why cant we use INA826 directly using the reference design in the INA826 data sheet for converting +/-20mV and +/-10V to +/-2.5+/-2.3V range.

  • 0
    Guru 140200 points

    Hi,

    the advantage of the circuit with the INA159 is that the INA159 is powered from the same supply voltage as the ADS1248. So there's no need to protect the ADS1248. When directly connecting the output of INA826 to the ADS1248 inputs, on the other hand, the much higher supply voltage of INA826 demands the installing of a protection scheme at the inputs of ADS1248. So, in any case you will need to increase R6 and R7 to limit the input currents of ADS1248 to below 10mA, better less.

    Kai

  • 0 in reply to kai klaas69
    TI__Genius 12415 points

    Hello,

    I agree with Kai here - in addition to his point about the supply voltage, the INA159 will attenuate by 1/5.  Since the input voltage specification is +/- 10 V (20 V pp), and the maximum input voltage to the ADS1248 is 5 V, it is necessary to attenuate the input to the appropriate input voltage for the ADS1248 by at least 1/4.  INA159 offers precision attenuation with integrated matched resistors to achieve 1/5 attenuation.  Since the minimum gain of INA826 is 1, it cannot be used for attenuation.

    If you are looking into a new design with INA826, you should also consider INA823.  INA823 is a newer version of INA826 that offers lower offset and lower supply operation.

    Regards,
    Mike

  • 0 in reply to Michael Hartshorne
    Guru 140200 points

    Hi Michael,

    I think Narashiman is referring to the circuit shown in figure 63 of datasheet of INA826 with the voltage divider at the input.

    Kai

  • +1 in reply to kai klaas69
    TI__Genius 12415 points

    Hi Kai,

    OK, that makes sense.  But as you know, one must be aware that the input impedance will decrease and the gain error will be degraded if matched resistors are not used on the inputs for that case.

    Narashiman, I'm going to close this thread, but let us know if there are any more questions.

    Regards,
    Mike

  • 0 in reply to Michael Hartshorne
    Prodigy 15 points

    Thanks a lot for your response. Will take this into my consideration for my design development.