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INA226 Alert Pin function

Justin Spence
Prodigy 30 points
Other Parts Discussed in Thread: INA226

Hi there,

I have a query regarding the the INA226 Alert Pin and the value used to assert it.

Datasheet: http://www.ti.com/lit/ds/symlink/ina226.pdf

The intention is to use the INA266 to perform over current detection by using the Limit Register and adjusting the conversation time and number of sample to average in the config register.

However, there appears to be conflicting information in the datasheet regarding how the Limit Register, Shunt Voltage register and Alert Pin work.

From Page 13:

“For example, if the alert function that is enabled is Shunt Voltage Over Limit (SOL), following every shunt voltage conversion the value in the Alert Limit Register is compared to the measured shunt voltage to determine if the measurements has exceeded the programmed limit.”

 From “Data Output Register”, Shunt Voltage Register page 20:

 “If averaging is enabled, this register displays the averaged value. Full-scale range = 81.92mV (decimal = 7FFF); LSB: 2.5μV”

 From “Data Output Register”, Alert Limit Register page 22:

 "The Alert Limit Register contains the value used to compare to the register selected in the Mask/Enable Register to determine if a limit has been exceeded.”

The text highlighted green indicates the Alert Pin will assert if the value sampled exceeds the value in the Alert Limit Register.

The test highlighted yellow from the Shunt Voltage Register and Data Output Register sections indicate that the Alert Pin will assert if the value in the Shunt Voltage Register (which is averaged based on the number of sample set in the config register) exceeds the Alert Limit Register.

Can you please clarify on what the intended operations is?

Thanks

Justin

  • 0
    TI__Genius 14825 points
    I believe you’ll find the answers in figure 19 on page 12. To the best of my knowledge, the Alert bit and pin set immediately after each conversion, not at the end of the averaging. This means that if a measurement ever exceeds the limit, you know about it.
  • 0 in reply to Jason Bridgmon
    Prodigy 30 points
    Hi Jason,

    Thanks for that. Unfortunately that is not how we initially read the datasheet. At least now we know that is the intended operation.

    I think the figure your refer to is supposed to be Figure 20 on page 10? It says “Current limit detect following every shunt voltage conversion". There is no option to set an explicit “Current Limit” on the “Current register”, only a “Voltage Limit” on the “Shunt voltage register” to be precise. So should more accurately read “Shunt voltage limit detect following every shunt voltage conversion”

    I do believe it would be prudent to have the datasheet updated to remove the conflicting information. I.e.

    For the Mask/Enable register’s description of the SOL bit – “Setting this bit high configures the Alert pin to be asserted when the Shunt Voltage Register exceeds the value in the Alert Limit Register.” And the Shunt Voltage Register’s description “If averaging is enabled, this register displays the averaged value.”

    Which is clearly contradictory, and indicates the Alert Pin will be asserted on the Alert Limit Register value exceeding the Shunt Voltage Register value which is averaged IF averaging is enabled.

    Thanks

    Justin
  • 0 in reply to Justin Spence
    TI__Genius 14825 points

    Justin,


    One thing I should mention, you're using the original data sheet, SBOS547.  I'm referring to the new one that was updated in June of 2015, SBOS547A.  You may find your recommendations for edits have already been incorporated in the revised data sheet.

    I hope that clarifies things.  Please let us know if you have further issues with the device, we're happy to help.