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Query regarding LM2904QDRQ1

Swati Jain1
Prodigy 50 points
Other Parts Discussed in Thread: LM2904

Hello,

I am using LM2904QDRQ1 in an application as a current sense amplifier.

I have a few queries:

a) The datasheet specifies the values of input offset voltage, bias current and offset current as follows:

 

Here, the minimum values (MIN) are not specified.

Could you please provide those values?

b) The input bias current values are specified as negative.

While doing analysis do I need to consider both positive and negative polarities?

c) Below is the circuit attached for reference and the equation used for output voltage.

Please see through and suggest if this is correct or needs to be updated:

Here,

Vout : output voltage of Opamp,

I.sense: current across resistor R4,

Vos; Input offset voltage,

IB: Input bias current,

Ios: Input offset current

R4: sense resistor

R1, R2; series resistors

R3; feedback resistor

 

Thanks a lot for your support.

Regards,

Swati Jain

 

 

  • 0
    TI__Guru**** 152966 points

    Swati,

    VIO is in the range of +/-VIO[max]. It can be positive or negative with no correlation channel to channel.

    IIB is always negative (conventional current flow out of the LM2904) and not zero. The minimum is -5nA. All four inputs will have a similar value. The maximum limits are much higher than needed, I would never expect more than half of maximum.

    IIO is in the range of +/-IIO[max]. It can be positive or negative with no correlation channel to channel.

    In the formula, change the "+" to a "-" for the IIB through R1. The voltages from IIB will mostly cancel when the effective input resistance are (nearly) the same.