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INA214: 3.3 and 24 supply

Erik Friesen
Prodigy 200 points
Part Number: INA214
Other Parts Discussed in Thread: INA219, INA190

Per the simplified schematic in the datasheet, how does this work to supply the device V+ with 3.3 and a common mode input voltage of 24V?  Its a little unclear in the datasheet how this is accomplished, as the common mode at the op amp input would be much higher than the supply. (According to the simplified schematic)

Typically there is some difference between rating and Absolute Maximum values, in this case 26V.  In order to follow transient voltage suggestions, this isn't so easy, as for example a 24V tvs doesn't have a very sharp knee, with the VBR starting well over 26V.  Any ideas on how this could be handled, or if it is necessary?

I'm using these with a 10mOhm sense resistor for a 2A range.  They will be upstream from a soft start PMOS switch.

  • 0
    Guru 140200 points

    Hi Erik,

    the answer is in the phrase "simplified schematic". The schematic is heavily simplified and not at all showing in detail what's internally going on. And don't overlook the magic box called "Bias" in figure 24.

    Kai

  • 0
    TI__Mastermind 18790 points

    Erik,

    Kai has hit the nail on the head here. Our devices utilize an internal biasing network on the front end that allows the inputs of the amplifier to be greater than the supply voltage. We typically only demonstrate this as a simple block diagram, as these are incredibly complex blocks of IP internal to the devices to handle these voltage differences, such as the one Kai points out in figure 24.

    Another (simplified) way to think of this block is as an internal switch that switches over when Vcm > Vs, and powers the amplifier via the inputs themselves, resulting in an increase in the input bias currents. You can see this in figure 11 of the datasheet. 

    The reasoning behind the absolute maximums and recommended values is many of our amplifiers have a "survivability" margin in case of overshoots in the common mode. In the case of the INA214, the device can withstand up to a 28V common mode, but the device is only guaranteed to work to 26V. You can see this footnoted in the abs max table, which I've highlighted below:

    Brass tacks, yes, this device (and many of our other current sensing amplifiers) can measure a 24V high side signal while the supply voltage is only 3.3V. If you think the common mode of your application is going to shoot past the 26/28V maximum, it may be more advantageous to choose a newer amplifier with a larger common mode capacity, such as the new INA241.

  • 0 in reply to Carolus Andrews
    Prodigy 200 points

    I don't know where you find the above mentioned screenshot, but the datasheet available here https://www.ti.com/product/INA214 doesn't match the specs are notes listed above.  Which will be right?

  • 0 in reply to Erik Friesen
    TI__Mastermind 18790 points

    Erik,

    Apologies, for some reason I had the automotive grade in my head, not the catalog part. The screenshot I took is from the automotive version of the part:

    The answer is that each of these tables are correct for their respective devices. For the catalog version of the device (INA214), the absolute maximum per pin is 26V. This corresponds to the voltage at each pin (IN+, IN-) with respect to ground, and are evaluated independently (not using the average of the 2). Let me know if that answers your question. Sorry for the confusion above. 

  • 0 in reply to Carolus Andrews
    Prodigy 200 points

    Well, it is rather confusing to have the absolute maximum the same as the rating on the device, it about makes me question the wisdom of using this part at 24v per the history of the a and b parts.

  • 0 in reply to Erik Friesen
    Guru 140200 points

    Hi Erik,

    section 6.3 of datasheet recommends the INA214 in applications with a common mode input voltage of +12V. There would be enough headroom to +26V and a TVS could easily be used.

    Kai

  • 0 in reply to kai klaas69
    Prodigy 200 points

    Your meaning is unclear.  Do you mean that I should not use this for 24V?  If you mean protect a 24V rail from Absolute max 26V with TVS, such a TVS doesn't exist.  I have 1K parts, maybe I should sell them.

  • 0 in reply to Erik Friesen
    TI__Mastermind 18790 points

    Erik,

    I'm in agreeance with you. The device's maximum is 26V, and 24Vcm is pretty close to the line. If you anticipate any fluctuation in the common mode, i.e., overshoot or transients, that could cause this voltage to transcend the abs max, there's risk of damage to the device, and there is most likely not a TVS that's going to kick in at the right spot to correctly deter the input without giving away at least some amount of marginal design room. A device capable of a higher common mode is probably the right design decision here.  

  • 0 in reply to Carolus Andrews
    Prodigy 200 points

    Well, I have 1K parts here I won't use.

    Also have 525pc INA219 I won't be using, which would appear to have similar front end with the INA214.

    I'd suggest this part gets a refresh, onsemi has a competing product with more realistic numbers, 30V abs max and 26 working voltage.

  • 0 in reply to Erik Friesen
    TI__Mastermind 18790 points

    Erik,

    We do have the INA190 available in a p2p SC70 that is capable up to 40V common mode that might serve better here given the common mode needs of your design. 

    Regarding the INA214, I've passed your feedback on to the systems team. Please let me know if we can help with anything else.