INA282: Min/max or standard Deviation of Differential impedance

SteeVeeDee

Part Number: INA282
Other Parts Discussed in Thread: MUX36D08, INA190

This INA282 data sheet states that the differential input impedance is typically 6 KOhm.

We would like to use the MUX36D08 in front of the INA282 to monitor currents on 8 different rails.

The MUX36D08 puts ~125 Ohms of resistance in series with each input of the INA282. Working against the input impedance of the INA282, this causes an error of about 4%.

We may be able to tolerate this and account for it, but it would be very useful to have some boundaries on the input impedance so that we can understand the boundaries of this error.

Can you please let us know if there is a min/max for the differential input impedance or a standard deviation that you can provide?

Thanks, best, Steve

over 6 years ago

0 Patrick Simmons over 6 years ago

TI__Mastermind 25145 points

Hello SteeVeeDee,

Thanks for considering to use Texas Instruments. The tolerance on the differential input impedance for the INA282 is +-15%.

If your common mode voltage for your rails is not negative, perhaps you may be interested in our INA190. This device has a very high input impedance and is also available with a 50V/V gain. The device currently is available for sampling and will officially release in about a month.

0 kai klaas69 over 6 years ago

Guru 140200 points

Hi Steve,

useful information can be found in section 7.3.3 of datasheet:

"Despite the use of internal zener-type electrostatic discharge (ESD) protection, the INA28x family does not lend itself to using external resistors in series with the inputs without degrading gain accuracy."

So, adding 125R series resistances from the mux is no good idea at all. This would be way too much.

Kai

0 SteeVeeDee over 6 years ago in reply to kai klaas69

Intellectual 700 points

Yes, thanks, I see that- but that is not the question I asked.

Do you have any estimate for the min/max of the differential impedance?

The precision requirement of this current monitor isn't particularly high. Also, it may be possible to calibrate it, so we still need min/max data to set limits on calibration.

Thanks, Steve

0 kai klaas69 over 6 years ago in reply to SteeVeeDee

Guru 140200 points

Hi Steeve,

as Patrick said: +/-15%.

Kai

0 SteeVeeDee over 6 years ago in reply to kai klaas69

Intellectual 700 points

Thanks; sorry, I only saw your response, not Patrick's! Doh!

0 SteeVeeDee over 6 years ago in reply to Patrick Simmons

Intellectual 700 points

Thanks; this is helpful. Unfortunately, one of the rails has a negative common mode, so can't use INA190 this time.

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INA282: Min/max or standard Deviation of Differential impedance