Current sense (shunt circuit)

Andrea B

Prodigy 20 points

Part Number: TLC2272
Other Parts Discussed in Thread: TLV2186, OPA2186, INA180, TLV2888

Tool/software:

Hi,

I'm looking for a reason of this issue:

I have the follow circuit to sense the current (shunt + OpAmp)

The OpAmp is a MCP6002 of Microchip
When there is no current flowing through the shunt R234 and R241, the voltage level on pin 1 of OpAmp is 0.06V and 0.6V on pin 7 of OpAmp.
If I use the TLC2272 instead of MCP6002 these levels of voltage are near 0V.

Why does the output voltage of the MCP6002 deviate from 0V

Best regards,

Andrea

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 320720 points

For support with Microchip devices, see https://www.microchip.com/en-us/support.

The TLC2272 has a lower typical input offset error. What is the maximum voltage over the shunt resistor, and the desired accuracy? What error can you tolerate at the inputs of the opamp?

0 Andrea B over 1 year ago

Prodigy 20 points

maximum voltage over the shunt resistor = 0.1V

desired accuracy = 5mV

error cat the inputs = 5%

+1 Clemens Ladisch over 1 year ago in reply to Andrea B

Guru 320720 points

The TLC2272 has a maximum offset of 2.5 mV, which is near your desired accuracy. The TLV2186 or OPA2186 would be more precise and cheaper.

Also consider an integrated current-sense amplifier like the INA180.

0 Art Kay over 1 year ago in reply to Andrea B

TI__Mastermind 27388 points

Andera,

I think in your original post your swapped your values. I think you meant that Pin 1 had 0.6V and Pin 7 had 0.06V. This would make sense as the gain of U21A is 10V/V, so 0.06V x 10 = 0.6V. Please confirm.
The microchip device has a maximum input offset voltage of 4.5mV. The gain of U21B is 22.1. This can product a maximum output offset of 4.5mV x 22.1 = 0.099V. So, you could actually see an output error greater than what you measured with the microchip device.
As Clemens mentioned the offset of TLC2272 is much better (2.5mV x 22.1 = 0.055V. Howerer you want better accuracy than this so you should consider TLV2888. It has a max offset of 0.015mV (0.015mV x 22.1 = 0.00033V.
In case you are not familiar with input offset calculations you can review this document: Op Amp Offset Voltage and Bias Current Limitations

Best regards, Art Kay

0 Andrea B over 1 year ago in reply to Art Kay

Prodigy 20 points

Hi Art, the values are swapped.

I will look for a device with a low "input offset voltage" than the microchip device.

Thanks.

+1 Art Kay over 1 year ago in reply to Andrea B

TI__Mastermind 27388 points

Andrea, Happy to help.

Best regards, Art

Amplifiers

Amplifiers forum

Current sense (shunt circuit)