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INA381: Gain change

Josef Muehlbauer
Prodigy 10 points
Part Number: INA381

INA381A1: 20 V/V

for some reason I had to increase the shunt resistor from 5mΩ to 10mΩ,  the max current should be 40A.

40A would generate 8V with gain 20, I am quite sure there is no possibility to realize this but perhaps there is a trick

to reduce somehow the gain or do you think it is possible to use a voltage divider for the voltage from the shunt?

thanks a lot for any answer

Josef 

  • 0
    TI__Mastermind 18780 points

    Josef, 

    You are correct in that the device will saturate above its supply rail of a maximum 5.5V, so 8V output will not be achievable. 

    You can reduce the voltage at the input pins by way of voltage divider, but this will be unattractive from a power perspective, as the resistors will consume additional power. With this in mind, the divider would effectively be stepping back down the sense voltage, can you elaborate on why you needed to decrease the shunt here?

    Another option that exists is to use the filter resistors to amend the gain, as discussed in section 8.1.4 of the datasheet. The challenge here is that the resistor network internal to the device is trimmed to itself rather than an absolute value, so up to 20% variation may be present from part to part. We have a great video here that discusses the challenges and limitations of such an approach, but know that this is typically not recommended if you need a precision measurement, as even at the new calculated gain, error from the network variation is substantial (normally 3-5%+).