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LM2904V: High Side Current Sense Output Issue

Part Number: LM2904V
Other Parts Discussed in Thread: OPA990, TL081H, INA180

Tool/software:

Hi TI,

I use LM2904V to design a high side current sense circuit.

I hand made a circuit and measure it, but output voltage is abnormal at Vbat lower than 12V as table below.

I would like to know why, which feature of OPA cause this?

Another question, why I can't use V+ lower than IN+? It also cause abnormal output voltage.

  • The LM2904V does not have rail-to-rail inputs; the input common-mode voltage range ends 2 V below the positive supply. Use something like the TL081H or OPA990.

    To be able to use input voltages above the supply, you need a specialized current-sense amplifier like the INA180.

  • Hi Sky,

    Clemens is correct. The LM2904V has some limitations that don't make it ideal for high side current sensing. It can be done by ensuring that the common mode voltage won't violate the datasheet but many times people just use a rail to rail device as it's easier to ensure it doesn't violate specs. 

    Thanks again Clemens for all your help on the forums. 

    Best Regards,

    Robert Clifton