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INA219: INA219 Application Questions

Part Number: INA219

Hello.  Some of these questions might have already been addressed, but after a quick search I couldn't find anything.

I'd like to use the INA219 in an project I'm working on and so far it seems to be working pretty well.  I have a few questions before I decide though.

1.   The INA219 is advertised as a high side current monitor, but is there any reason I can't use it as a low side monitor?  In my application, I have the chip set to the 320 mV FSR, and I'm using it to sense a 4 - 20 mA signal across a 10 ohm shunt resistor.  I've tested it on the low side and it seems to work fine.  I understand the INA220 is almost identical, and can also be used on the low side, but it's slightly more expensive. So, is the INA219 just less accurate on the low side because of the lower common mode voltage, or is there another reason it's not advertised to work on the low side too?

2.    I'm planning on protecting the inputs with a TVS diode and RC filter like the datasheet describes, but when I tried to breadboard the RC filter the reported measurements became very inaccurate and unpredictable.  I used a 10 ohm resistor in series with each input, and a 100 nF capacitor across them just like it's shown in the datasheet.  This was with the same 10 ohm shunt resistor.  My question is, can the inaccuracy be explained by input resistors that weren't evenly matched (either because of the tolerance or the solderless breadboard)?  Or, are problems created when the series input resistors are close in value to the shunt resistor?  In the datasheet, the shunt resistor is in the milliohm range, so the input resistors (10 ohms) are orders of magnitude above that.

3.    What is the significance of the 'A' and 'B' suffix in the part number?  I'd like to choose the part that is more ESD resilient, and can tolerate more/greater dV/dt events.  Does this suffix have anything to do with that?

Thanks in advance for any help you can provide.

  • Hi Joshua,

    That's a good question. I will seek clarification on whenever the device can be used on the low side as well. From a first look, it appears that as long as the IN+ and IN- Inputs are correctly wired there should be no issue.

    The input resistors should have no effect. They are only there to avoid excessive current caused when the built in ESD protection is activated. This can occur, for example, in situations where a large dv/dt occurs, such as the large current flow to/from an electrolytic capacitor. I would recommend making sure the issue is not caused by the breadboard itself and removing/choosing a lower value capacitor in series with the input

    Lastly, the B grade version is trimmed for a higher accuracy level. For example, the offset voltage and measurement error over temperature are essentially half of that on the A version. Please refer to the electrical characteristics section of the datasheet for a full list of differences.

    Kind Regards,

    Carlos S., TI Sensing Products, Applications Support

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Carlos Silva85:

    Carlos,

    Thanks for your reply.

    I’ll wait to hear back from you about the low side usage.  With respect to correctly wiring the IN+ and IN- terminals, as long as I ensure that the common mode voltage applied to each is greater than -0.3V, I should be able to connect the IN+ and IN- to either side of my current shunt resistor since the differential voltage limit is +/- 26V.  Is that correct?  Please let me know if I’m misunderstanding these limits.

    About the input resistors, did you mean to write “removing/choosing a lower value resistor in series with the input”?  I have no capacitor in series with the inputs.

    Lastly, I see the distinction between the A and B models in the datasheet now.  Thanks for pointing that out.

  • In reply to Joshua Moskowitz:

    That is correct. The only difference is the way the connections are done. On a low side, IN- connects to GND side and IN+ to the load side of the sense resistor, whereas on high side the IN+ is connected to the supply rail side and IN- to the load side of the sense resistor.

    No, the datasheet shows the two 10ohm resistors in series with IN+ and IN- and a capacitor in parallel with the inputs. The resistors should be kept, but the capacitor value may be changed depending on the filtering requirements. If you don't have any and are experiencing problems then the issue lies on the breadboard connections.

    Kind Regards,

    Carlos S., TI Sensing Products, Applications Support

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Carlos Silva85:

    Carlos,

    Any word on whether or not it's OK to use the INA219 on the low side as well?  My testing seems to indicate it will be OK, but I'd like to hear it from you guys before I send my boards off to be made.

    Thanks.

  • In reply to Carlos Silva85:

    Bump.

    Hey Carlos,  any word on using this part on the low side?

  • In reply to Joshua Moskowitz:

    Hi Joshua,

    Thank you for bearing with me while I checked into this.

    I can confirm, unless otherwise noted, all our current sensing devices are able to operate on low side. Some exceptions are the INA13x/16x and 216.

    Kind Regards,

    Carlos S., TI Sensing Products, Applications Support

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Carlos Silva85:

    Carlos,

    No problem. Thanks for the verification. I'll be using the INA219 on the low side in 2 circuits.
  • In reply to Joshua Moskowitz:

    Coming to this a bit late, but the issue on low-side with the INA219 is that it cannot be used to calculate power when on low-side as the VBUS pin and VIN+ are the same.  The INA220 has a separate VBUS pin from VIN+ to allow it to be used on low-side while also able to calculate power consumption.

    Regards, Dan