Part Number: INA181
for a bidirectional current sensing application I'm using an INA181.I'm sensing the current in- and outflow of a leadacid-battery, so approx. 12V. As a µC I use a CC2640R2F.I applied 3.3V to VS, ~12V to IN+ and IN- and gave it as a reference the VDDR pin of the CC2640, which is ~1.7V, the output goes directly to an analog pin of the µC.There are two problems occuring:
1. When my board is completely switched off, but the 12V on IN+ and IN- still applied, there is a Voltage on VDDS present, which I don't want. If switched off, the board is required to carry no voltage at all (but the 12V) .
2. After a while the INA181 heats up (you can't touch it with the finger), and eventually it broke due to overheating.
So my question is, is there anything I'm missing out on? I sticked to the datasheet as close as possible, but the INA181 shows the stated behaviour. Maybe using the VDDR pin of the CC2640 as a reference was a mistake, would that explain it? Any suggestions on how to make it work on the prototype?
Any help is highly appreciated, thank you. Alex
In reply to Alexander Gemmer:
Hey Alex, That is correct, when there is only voltage at IN+ and IN- then OUT, VS, and REF should all be 0V. I look forward to hearing how those tests go.
Mitch M, TI Sensing Products Applications Support
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In reply to Mitch M:
today I received the order of some more INA181 devices from TI-Store. I soldered a device on my PCB with no parts on it at all, but the INA181 and shunt. I then applied 12V to IN+ and IN- and measured the outputs.
VS = 1.468VOUT = 1.468VREF = 11.19V
None of the pins have a physical connection to each other on the board in this setup.I then measured the Pin-to-Pin resistance.
Soldered on the board:
OUT - IN+/IN- --> ~500 kOhmREF - IN+/IN- --> ~500 kOhmVS - IN+/IN- --> ~9.6 MOhm
The IC just itself NOT soldered on the board:
OUT - IN+ --> ~500 kOhmOUT - IN- --> ~500 kOhmREF - IN+ --> ~500 kOhmREF - IN- --> ~500 kOhmVS - IN+ --> ~9 MOhmVS - IN- --> ~9 MOhmIN+ - IN- --> ~2.5 kOhm
As you stated above the Pins VS, REF and OUT are supposed to show 0V, which is not the case right out of the box.The functional block diagramm in Figure 39 in Section 8.2 of the datasheet shows probably the resistance I measured.
I'm confused, maybe this information tells you something.Regards, Alex
it's good to know, that the parasitic voltage is normal. I now approached the intended configuration step by step by soldering a INA181 to a fully functional board. I first applied 12V to common mode, which was fine, then I switchen on the whole board, that worked out as well. I then applied 3.3V from the Launchpad via JTAG, that was fine too.
The measured voltage on OUT fits perfectly to the applied current to the shunt.So my guess is, that probably either the first IC that I used was broken, some ESD issues occured or I messed up something when soldering it.It's a bit unsatisfying, because I can't recreate the overheating and thus never know what actually happened. But on the other hand two of my boards now work as intended for some hours without any problems.I'd like to thank you for your help, that is much appreciated. And after all, it didn't work in the beginning and now it does and you were a great support on the way!Thank you!
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