Regarding current sense

[NJani.2]

Hello Support,

I have application in wjhich i have to sense current for negative supply. specifications are as below.

Negative supply voltage range( at RS- pin) : -5 V to -2 V

Current range that needs to be sensed: 0.1 uA to 20uA

The output of OPAMP needs to be read by 10 bit ADC of controller. 

we have one application note AN4451 in which it shows nA range. but in our application the voltage is negative so please guide regarding that or suggest some part number.

Thanks

[NJani.2]

Hello,

Thank you so much for your valuable support.

We have gone through the details given from your side and come to a conclusion to TSZ121 low side configuration may be the best suitable to our requirement. as in high side, there is a chance of error as per given in your PPT.

Please find below diagram and verify whether it is ok or not? or any further modification and suggestion is required.

Once you confirm, we will finalize this op-amp.

Once again, Thanks for your guidance .

[AUPETIT nicolas · Accepted solution]

​Hello

A last point to check. It is the current sense you have to measure. As the lowest potentential is the power supply -5V, the current should flow from ground to power supply isn't it? So in this case, connection should be like this:

If you need to use the current sensing  only in monodirectionnal mode, and so don't need the Vref on the schematic above, you can even save two resistances as depicted by the below picture.

Precision will be even better with 2 resistances rather than 4 resistances ( as error is mainly due to the mismatch of the resistance)

BR

[NJani.2]

Hi Nicolas,

Thank you so much for providing valuable support to select best OPAMP for our project.

Yes current flow from ground to power supply. As per your suggestion we will use 2 resistor 1K and 15K with feedback in low side configuration.

Kindly suggest if any other things need to add or verify.

once again thank you for your support.

Thanks