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# INA169: INA169 minimum voltages

Part Number: INA169
Other Parts Discussed in Thread: INA190, INA191

Hi team,

Good day.

What is the minimum (step) differential voltage that INA169 can detect? What is the minimum sense voltage we can provide to INA169 without any error and how to calculate for the value?

Regards,
Carlo

• Carlo,

When you say smallest here, are you asking in terms of resolution, i.e., something along the lines of an LSB? Or, are you asking with regard to the offset, i.e., the smallest V_SENSE that can realistically be measured by the device?

Can you share your use case and what you are trying to measure here?

• Hi Carolus,

Our customer is referring about the smallest Vsense voltage that realistically can be measured by the op-amp. Is it 100mV? Is the calculation for this is VSENSE = VIN+ – VIN–?

Regards,
Carlo

• Carlo,

So this is tough to answer with a flat value. First, there is no such thing as a measurement with no error. There will always be error present in a measurement, and the customer is going to need to determine the level of error that is acceptable. When dealing with amplifiers, this will come from several sources, including the device's voltage offset, CMRR/PSRR, gain error, shunt resistor tolerances, and gain resistor tolerances, just to name a handful.

For example, here is a worst case error curve for the INA169, in a use case where the common mode is set at 12V, power supply to the INA169 is 5V, and the shunt is a 20mohm shunt with a 0.1% tolerance. With these points, error from common mode and power supply rejection error is 0. The error curve looks like this:

Across the 20mohm shunt, 2.5A would exhibit a 50mV V_SENSE, and the total output error would be just under 3%. As the sense voltage grows smaller, this error will exponentially grow, as the offset voltage increasingly dominates the measurement. As the measurement grows, the gain error worst case of 2% is now dominating, and this is why the curve cannot get better than this amount of error.

In summary, you need to understand how much error the customer is willing to tolerate to determine the "smallest" value they can realistically measure. Does that make sense?

Again, if you can share their use case, I can help with part selection or error analysis to meet an error budget. Let me know how I can help.

• Hello Team,

We are looking for a Instrumentation Amplifier/current sense monitor to sense the current as low as 0.1mA to max 500mA range, the input Vsense (differential) voltage for op-amp is as low as ~0.1 to 0.2mV with suitable sense resistor.
Please provide the instrumentation amplifier parts from analog which can measure/sense the minimum voltage of 0.1mV and also shall be able to measure max of 500mA of current. Currently INA169 from TI is being used in other designs which is not exact to our above specs in the new design.
Thank you.

• Mahender,

For current measurement this low, I would recommend checking out the INA190 and INA191. These are precision current shunt monitors with picoamp bias currents that will minimize the effects of the front end on a current so small. That said, this is still going to be a very challenging system to design due to the wide range of the FSR you are attempting to measure here (5000:1). With a 5V supply and the G=20 variant, VSENSE on the lower end would be .5*.0001 = 50uV if you use a 500mohm shunt, and the output of this would be 10mV. This looks like it would be above the swing to GND limitation of the device. The main issue here, as I mentioned above, is the error. The worst case offset of this device is 12uV, which is potentially 25% error on the lower end (typical is 2.5uV, or 5% error). You would need to to perform error analysis with this device to ensure the FSR% error is acceptable.