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INA240-Q1: Effect on Output Bias voltage by Common mode voltage shift

NOBUO FUJIHARA
Genius 9365 points
Part Number: INA240-Q1
Other Parts Discussed in Thread: INA240

Hi Team,

My customer is investigating to use INA240 for 100's A order current measurement application.

They wants to supply output bias current of 2.5V by the configuration seen in Figure 29. "Midsupply Voltage Output".

Please see attached figure.

In the figure, VCM is cell voltage and varies from 10V to 12V.

Due to this VCM shift, customer concerns output bias voltage (ideally 2.5V) may shift.

I suppose effect on Vbias by VCM shifts would be mainly affected by 50k/(R1+R2), could you provide relation or data on this?

Best regards,

  • 0
    TI__Mastermind 34560 points

    Hi,

    The customer’s concern is understandable, but not necessary. Here are a couple of key points to keep in mind when considering the impact (or not) of “VCM”

    First “VCM” is effectively decoupled from the output stage by the input which is fully differential. As a result the common mode input voltage to the 2nd stage is independent of “VCM”. Granted that it will move up or down relative to ground based on differential input voltage, but the range is much limited, between ground and supply VS.

    Second, when the common mode input voltage(again, not because of VCM) to the 2nd stage changes, it is correct that “VBIAS” will move as a result, however this is a common mode effect and will be cancelled out at the device output. This behavior is different from that if “VBIAS” changes as a result of changing REF1/2. It is a result from the difference amplifier operation.

    Regards, Guang

  • 0 in reply to Guang Zhou
    TI__Genius 9365 points
    Hi Guang,

    I wold like to move to offline discussion via e-mail for further question.

    Best regards,
  • 0 in reply to NOBUO FUJIHARA
    TI__Mastermind 34560 points

    Hi Fujihara-san,

    Since we’re working on this offline, I’ll close the thread. Please feel free to click the “this resolved my issue” button when you’re ready

    Regards, Guang