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INA500: INA500C Max Input Voltage

Varunesh Kumar
Intellectual 980 points

Part Number: INA500
Other Parts Discussed in Thread: TINA-TI

Tool/software:

Hello

I am proposing to use INA500C operating from a 3.3 V PS, and to transform a +/- 6V to 0-3.3 V using

This Difference Amp and using a Ref of 1.65 V

Would there be any issue with a Vin of +- ^ to the Input pins?

Thanks

Varun

  • +1
    TI__Intellectual 1240 points

    Hi Varun,

    Do you know what the common mode of the +/-6V signal is? With the a 3.3V V+ and V- set to GND, if it is just a +/-6V signal on In+ and In- is grounded, there will be no issue with the input common mode requirements. You can use the following equation in the datasheet to see if the design fits the input common mode requirements of the difference amp. For this application, it is -6.6V to 9.9V.

    The output equation of this diff. amp is Vout = 0.25(Vin+ - Vin-) + Vref. So with a +/- input of 6V and Vref of 1.65V, the output is going to range from 0.15V to 3.15V instead of 0V to 3.3V.

    Also, there are two output voltage requirements to keep in mind for the INA500. Firstly, there is the output headroom, which is the maximum voltage from each supply that you can  output based on the output stage transistors in the op amp. These are shown below.

    However, you cannot expect that the INA500 will be linear for that range. For a linear output, you have to refer to the gain error test conditions (shown below), which specify a certain gain error for an output range. The output should be linear for this range.

    If what I have assumed is correct, the INA500C should fit very well for this application if you want an output ranging from 0.15-3.15V.

    You can use TINA-TI or PSpice for TI to test your design, as it accurately simulates the input/output requirements of our devices. Below shows a quick simulation I did showing the input/output of your design.

    Best Regards,

    Taylor Allan

  • +1 in reply to Taylor Allan
    Intellectual 980 points

    Hi Allan 
    Thank you for your quick reply. 

    I was looking at the Abs Max Value at the Input Pins

    Yes, my Ckt shall be the same as shown by you, that is

    the INV Input as GND and the NI Input fed that +/-6 to 7.5 V 

    peal to peak. Vref as 1.65 V 

    While comparing with INA600x, I was trying to look for the 

    Max Input Voltage that I could feed to the NI Input, and possibly

    mistakenly I read that as limited to thr Supply Voltage 

    I went back to read that and found that 

    "  The device can handle up to 27.5V (±13.75V) of input common-mode

        voltage in G = 0.25 with 5.5V (±2.75V) "

    So all is well, and it was my mistake..

    Thanks again

    Varun