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# INA2180-Q1: accuracy impaction by Zener diode&R

Part Number: INA2180-Q1
Other Parts Discussed in Thread: INA2180, STRIKE, OPA2192-Q1, OPA2192, INA2290, INA2191

Dear expert,

Customer is using INA2180A3-Q1 for high side current measurement. Vbat is 9V~16V.  Current is from 1A~30A. Current sensor resistor is 3mohm. Battery voltage is 9-16V.  ADC is 0~5V range.

For "load dump" test, Vbat can reach 36V max. To protect INA2180. Customer add 1K resistor + Zener diode(BZX84_B24) to GND before INA+/-. (They cannot add TVS at Vbat directly due to other concern.)

Do these 1K resistor + Zener diode(BZX84_B24) impact INA2180A3-Q1 accuracy? And how to calculate?

Thanks

• Hello Ryan,

We do not recommend resistors above 10Ω.  We have a calculation for Gain error on page 23 of datasheet.  Equation number (4) with example calculations in on table2 below that equation.

• Javier,

Or do you have another part to recommend which can survive from 36V strike at IN+/IN-?

OPA2192-Q1 can meet requirement but is too expensive. They want something cheaper.

Thanks a lot

• Hi Ryan,

if I may add something: Additionally to that the filtering resistors should not exceed 10R for gain error reasons, the problem is that any imbalance introduced by the two protection schemes will ruin the awesome common mode rejection of INA2180. Usually, there's only the very small shunt between the inputs allowing both inputs to see a very similar or even identical source impedance situation. This allows highest common mode rejection. But if you add protection diodes with uneven junction capacitances being isolated by current limiting resistors, both inputs see no longer identical source impedances and the common mode rejection is ruined. Of course, you can do some fine trimming with adjustable capacitances or hand selection of TVS for identical performance but this is hardly something for mass production. Also, the fine tuning of input capacitances will depend on the actual mounting and cabling conditions.

Take care, load dump protection is difficult because of the enormeous energy of the load dump pulse. This cannot be done with 10R resistors. Because of that many cars provide a central load dump pulse protection. So, are you sure that your circuit has to withstand the full load dump pulse at all?

Kai

• Kai,

Thanks a lot for your comment.

• Kai,

So do you have another part to recommend which can survive from 36V strike at IN+/IN- other than OPA2192 which is too expensive?

• Ryan,

I would go through the parametric search as it also has cost as a filter/sort.

https://www.ti.com/amplifier-circuit/current-sense/products.html

This link below is only devices with VCM above 36V.  The biggest issue is the dual option.

https://www.ti.com/amplifier-circuit/current-sense/produwcts.html#p726max=36;120

With dual options you have the INA2290 and INA2191