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INA240: Use in bipolar mode with + and - supply

Part Number: INA240
Other Parts Discussed in Thread: INA282,

is it possible to use the INA240 or INA282 in a configuration where the GND pin is a -Vs, supply at +Vs and REF1=REF2 = 0V = GND? (Vs=½(2.7V to 18V) = Dual supply = Split supply. Both parts are meant to be used in single supply mode.

I am concerned by the noise which typically will be present on the -Vs rail (similarly to the noise on +Vs) if that will couple into the signal. Because the PSSR is (obviously) not specified for this GND referenced part. As far as I can tell - DC wise it should work fine though.

The reason is that all my other parts are bipolar operation around 0V.

Any ideas are helpful.

  • Hi Henning,

    The answer is yes, you can use dual supplies. Just treat the negative potential as device ground in all calculation.

    Total supply wise, INA282 can operate from 2.7 to 18V. However INA240's operating range is 2.7 to 5.5V. As long as the datasheet operating conditions are not violated, you’ll be fine.

    Regard, Guang

  • Thanks Guang,
    Right - i overlooked the Vs amplitude limit.
    But "treat the negative potential as device ground in all calculation" I am not sure I understand. I would expect to have to use the REF1=REF2=0V as the reference. So when input (IN+)-(IN-) = 0 <=> Vout = REF1=REF2=0V . So in fact the negative device potential is irrelevant. Is that incorrect? If yes, then I miss something.
    br henning
  • Hi Henning,

    That statement might be a bit misleading, sorry. What I meant was now that device ground is negative, -2.5V for example, other pin potentials must be calculated relative to -2.5V.

    Additionally, if Vsense=0V and REF1=REF2=0V, then Vout=0V. The transfer function in this configuration would be: Vout=Gain X Vsense, where obviously Vout is also bounded to ~(-2.5V, 2.5V).

    Regard, Guang

  • Thanks again Guang,
    I just realize that the parameter I was looking for: the power supply rejection ratio (PSRR) for the negative supply in this +-Vs supply mode is actually the Reference voltage rejection ratio (RVRR) in the datasheet.
    So for instance with RVRR = 20uV/V = -94dB, (INA240A1 ) a ripple on -Vs of 1V will transform to a ripple of 20uV on Vout. And similiarly for +Vs but then it is the PSRR which is the gain value. Am I right?
  • Hi Henning,

    Not exactly.

    RVRR is “reference rejection ratio”, if there is a 1V ripple on REF pins (REF1=REF2=Vs/2 as spec table says, which equals 0V nominally in your configuration), it will cause a 20uV input referred ripple. When translated to output, it is Gain X 20uV. Hopefully you don't have such a big ripple to begin with, otherwise you'll need a better reference!

    PSRR is 10uV/V, therefore a similar amplitude ripple on either rail will cause an output ripple of Gain X 10uV. Again hopefully in reality the ripple on either rail is much smaller.

    The two of them have no direct relationship.

    From the INA’s perspective, your configuration is identical to spec table test condition, the only difference being common mode voltage potentially. If you have a common mode of 9.5V then everything should be identical. 

    Regard, Guang