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LM7301: LM7301 application

Gholam
Prodigy 110 points
Part Number: LM7301
Other Parts Discussed in Thread: INA148, INA149

Tool/software:

Hi,

I would like to use this circuit for a ±10V input range while connecting -AIN to the ground.

I was wondering why a +1.5V offset is used on the positive input, and how the gain can be calculated.

For a +10V input, what would the output be?
For a -10V input, what would the output be?

Thank you,

  • 0
    TI__Guru 63611 points

    Hi Gholam,

    Gholam said:
    For a +10V input, what would the output be?
    For a -10V input, what would the output be?

    Here is the simulated results and it seems to be linear and acceptable. 

    LM7301 DA 12052024.TSC

    Please make sure that you need to consider the Vout output voltage swing and do not get to close near the GND. 

    Please make that the Vref node has to be low output impedance and it is capable to source and sink current for proper operation. Below is an example, but most op amp should work for supply the Vref voltage. 

    If you have other questions, please let us know. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 110 points

    Hi Raymond,

    Thank you for your reply.

    Could you please explain how this circuit works? I would like to understand the logic behind it, the reason for the 1.5V offset, and how to calculate the gain.

    It would be great if you could walk me through the circuit step by step.

    Thank you!

  • 0 in reply to Raymond Zhang1
    Prodigy 110 points

    Would you please elaborate on the calculation of Vdiff? I can't understand how is -8.64 when the input is -10.

  • 0 in reply to Gholam
    TI__Guru 63611 points

    Hi Gholam,

    Gholam said:
    Would you please elaborate on the calculation of Vdiff? I can't understand how is -8.64 when the input is -10.

    This is interesting properties of difference amplifier, where Vout = Gain*(Vin_p - Vin_n), see the simulation below. 

    LM7301 DA 12052024 option3.TSC

    In similar application, we have INA148, INA149 and others that use this feature to interface with higher common mode voltage than an op amp's supply voltage. The example below is from INA148 in Figure 3. 

    https://www.ti.com/lit/ds/symlink/ina148.pdf?ts=1733462659753

    If you have other questions, please let us know. 

    Best,

    Raymond