INA2181: VREF pin input impedance and external circuit

TomokiP

Part Number: INA2181
Other Parts Discussed in Thread: TINA-TI, INA181

We are designing a current sensing circuit with an output offset given by VREF pin.

Is the buffer circuit (highlighted in the screenshot) connected to VREF pin mandatory? Can we directly connect the resistor divider network to VREF pin?

In other words, what is the input impedance of VREF pin? I could not find any information on its datasheet.

Thank you for your support.

Best regards,

over 1 year ago

+1 kai klaas69 over 1 year ago

Guru 140200 points

Hi Tomoki,

I would run a TINA-TI simulation to see the effect of added voltage divider resistance:

Kai

+1 Cierra Cowley over 1 year ago

TI__Intellectual 1235 points

Hi Tomoki,

Yes, the buffer is required if using a resistor divider for the reference voltage. If not, the resistance from the divider will contribute to the internal resistance and shift the balance of the resistor network. This will cause the gain/output voltage to shift as Kai has shown in the provided plot.

This app note gives a detailed analysis as to why using a resistor divider without a buffer should be avoided: Driving Voltage Reference Pins of Current Sensing Amplifiers

Please see Section 6.1 for an analysis of INA181.

Please let me know if you have any other questions.

Cierra

0 TomokiP over 1 year ago in reply to kai klaas69

Prodigy 20 points

Thank you for your clarification.

The simulation is very clear!

Best regards,

0 TomokiP over 1 year ago in reply to Cierra Cowley

Prodigy 20 points

Thank you for linking this application note: very complete!

Best regards,

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INA2181: VREF pin input impedance and external circuit