INA138: Current Read Out Accuracy Issue

Ben CHEONG

Part Number: INA138
Other Parts Discussed in Thread: INA139

Hi TI support Team,

Good day.

We have been using INA138 for quite some time, but recently the current reading detected from production is getting higher.

I would like to know the current range reading calculation will just base on gm highest = 202uA/V Typ = 200uA/V Min = 198uA/V ?

Rs = 2mOhm

RL = 200KOhm

IS	Vout (Typ)	Vout (Min)	Vout (Max)	Good Part	Within Specification	Faulty Part	Out of specification
0.3	0.024	0.02305	0.02472	0.0231	OK	0.038	NG
0.6	0.048	0.0461	0.04945	0.0462	OK	0.062	NG
0.9	0.072	0.06916	0.07417	0.0693	OK	0.093	NG
1.7	0.136	0.13063	0.14011	0.135	OK	0.152	NG
3.2	0.256	0.24589	0.26373	0.246	OK	0.271	NG
4.6	0.368	0.35346	0.37912	0.361	OK	0.39	NG
6.1	0.488	0.46872	0.50274	0.48	OK	0.509	NG
7.7	0.616	0.59167	0.63461	0.599	OK	0.628	NG
11.4	0.912	0.87597	0.93955	0.896	OK	0.927	NG

Based on the calculation, the previous batch we have used is all within the calculation, however the recent batch INA138 calculation is all out of the range. would it be normal?

Measure by Meter (A)	Measure by Good Part (A)	Measure by Faulty Part (A)
0.3	0.342	0.564
0.6	0.533	0.876
0.9	0.916	1.269
1.7	1.662	2.014
3.2	3.173	3.515
4.6	4.663	5.016
6.1	6.164	6.527
7.7	7.665	8.028
11.4	11.433	11.815

Seem like the new batch IC is having higher reading compare previous batch IC.

any advise on this?

Thank you

Ben

over 2 years ago

0 Javier Contreras4 over 2 years ago

TI__Mastermind 29280 points

Hello Ben,

Have you performed and A-B-A swap to verify there is no issue with the board or larger resistance than expected. https://training.ti.com/zh-tw/troubleshooting-tips-ic-b-swap?context=1140237-1138746-1139731-1138742

From my experience with the INA139 or any current out device I have seen leakages or larger resistances than expected causing the error. Doing an A-B-A swap could help determine if there is another issue. If you do not see any issues with an A-B-A swap please share a schematic or more to determine what other items could be the issue.

0 Ben CHEONG over 2 years ago in reply to Javier Contreras4

Prodigy 100 points

Hi Javier,

Thank you very much for your prompt reply.

Yes, I have performed A-B-A swap to verify. The symptoms is following the IC, the IC which is having high accuracy remain accurate reading, and the IC which having high tolerance remain reading higher than expected.

This INA138 IC have been using nearly 5 years, in the past it was giving high accurately of current reading, just recently I am facing current reading higher than expected. circuit design and PCB layout are the same and already use for 5 years.

Thank you

Ben

0 Javier Contreras4 over 2 years ago in reply to Ben CHEONG

TI__Mastermind 29280 points

Ben,

I think this is due to the VOS of the device. I did not realize initially as I looked at only the variation from good to bad. I believe that this is the same data from you and it came from some one else. See this post. https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1057329/ina138-if-our-vin-is-under-22-mv-would-you-please-help-to-check-my-tested-results-were-acceptable-or-not

0 Ben CHEONG over 2 years ago in reply to Javier Contreras4

Prodigy 100 points

Thank for you reply Javier, this might be the distributor. Before I post to the forum, I share the same information to distributor as well

0 Javier Contreras4 over 2 years ago in reply to Ben CHEONG

TI__Mastermind 29280 points

Ben,

Please let me know if you have further questions. If you need a device with better VOS please let me know what your other requirements are and I can assist in finding a device.

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INA138: Current Read Out Accuracy Issue