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• TI Thinks Resolved

# INA149: MIN and MAX values of input differential impedance

Part Number: INA149

Hi Team,

Do you have the min and max values of input differential impedance of INA149? Datasheet only shows 800 kohm, which is the typical value.

I'm asking this because my customer will need to specify input impedance in their datasheet and now they measured something around 755 kohm, and are not sure if that's reasonable or not.

Thanks!

Roy

• Hi Roy,

Thank you for your question, I can help you. We do not have the min and max values for differential input impedance, we only have and specify typical. The differential input impedance is defined as the sum of the input resistors. However, it is important to note that the resistors you see in the INA149 are ratio-metrically matched to achieve unity gain, but may vary up to 15% (in either direction). This means that the absolute value of the resistors between lots fabricated at different times may vary up to +/-15%, but the matching is trimmed to 0.005%.
Hope that helps!

-Tamara Alani

• In reply to Tamara M Alani:

Hi Tamara,

By "This means that the absolute value of the resistors between lots fabricated at different times may vary up to +/-15%", is it equivalent to saying that the differential impedance can be in the range of 680 khom to 920 kohm?

Thanks.

Roy

• In reply to Roy Hsu:

That's correct.

-Tamara Alani