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INA149: Single Supply Differential input voltage

Part Number: INA149

Hello,

design a high side current monitor (200V), I was looking to use INA149 but a single supply configuration (+5V).

The datasheet presents the following conditions with Vs=+5V, REFA=REFB=2.5V. I understand the limitation on the common mode voltage but I don't understand the differential range limitation.

Can you, please elaborate on this parameter ? does it mean, we cannot measure difference (V+-V-) lower than 1.5V ? Is there an equation or rule of thumb defining this range ?

The Vcm is driven by this equation VCM (±) = 20 VX/VY(±) − 19 VREF while Vx and Vy are the maximum output voltage, in components similar to INA149. Is this correct too?

thanks for your answer and feedback.

Yours Sincerely,

 

  • Hello Mohamed,

    The differential input voltage range is the voltage difference, positive to negative, or negative to positive, that can be applied across the inputs for linear operation. The common-mode voltage range is the range of voltage for an equal voltage that can be applied to both inputs and the very high common-mode rejection ratio (CMRR) is maintained.

    There appears to be a problem with the INA149, Vs = +5 V (Vref = +2.5 V) table with regard to the differential and common-mode input voltage ranges. The INA149 has internal input and output node limits of +1.5 V to +3.5 V, (Vs = +5 V) to assure linear operation. That is reflected in the Output Voltage range specification, and was possibly the intention of the Input Differential Input Range specification. Therefore, the combination of the differential input voltage (Vdm), common-mode input voltage (Vcm), and Vref must not result in voltage levels that are outside of the +1.5 V to +3.5 V internal node limits.

    An idealized INA149 TINA Spice simulation circuit was created to observe the input and output node voltages for any combination of Vdm, Vcm and Vref. The simulation circuit could be used check the nodes to be sure the limits weren't being exceeded.

    The first entry in the table above is for the condition where Vcm = 0 V. The Vdm is limited to +/-1 V because the output node is limited by +3.5 V, or +1.5 V. The second set of entries show the condition for Vdm = +/-1 V, the lowest negative Vcm is -18.5 V in that case. Similarly, the third set of entries is for the highest positive Vcm of +23.5 V. Different combinations of the voltages can be tested. The TINA circuit file is included here:

    INA149_ideal_01.TSC

    It would not be possible to use the INA149 in a 200 V Vcm application with a single +5 V supply. It would be completely applicable in that application if +/-15 V supplies are used because the internal node limit voltages are much higher.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • Thanks a lot for these insights.