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INA228: P_TME of the INA228

Alex LeBlanc
Prodigy 100 points
Part Number: INA228

The voltage and current sense gain errors are quite low (±0.01% typical, ±0.05% max), but the power total measurement error is quite high (±0.5% max).    

Where is all this error coming from?

For my application, I'll be sensing (high-side) a 1A current through a precision 0.1Ω resistor (so 0–100mV shunt voltage) with 1–10V bus voltage. What kind of power measurement accuracy and precision can I expect (in mW)?

Also, it's a bit of a shame that there's no internal gain setting for the bus voltage; seems like we lose an awful lot of our precision by working at an eighth of the max.

  • 0
    TI__Expert 6602 points

    HI Alex,

    The P_TME spec is gathered by combining the error sources for both the VBUS and Vshunt combined. It is the total power monitoring accuracy for the part. In order to calculate error and view error sources with detail along with comparison to other parts, you can use our error calculation tool: https://www.ti.com/tool/CS-AMPLIFIER-ERROR-TOOL. 

    Best,

    Mohamed

  • 0 in reply to Mohamed Hamida
    Prodigy 100 points

    Even with the current sense at 0.05% and voltage sense at 0.05%, I'm not understanding how the power measurement would have 10x the maximum error of the voltage and current measurements. Even at worst case, (1+0.05%)*(1+0.05%)-1=0.1% (approximately).

    There must be other factors?

    What would be the power measurement error for the values I indicated above (0.1Ω resistor, 0-1A current, 1-10V bus voltage)?

  • +1 in reply to Alex LeBlanc
    TI__Expert 6602 points

    Hi Alex,

    As the datasheet notes, the spec is mentioned over temperature. After speaking with a systems engineer, I learned that 20ppm over 100C will add 0.2% error. The 0.05% error for current and voltage sense is spec'd at room temperature. Over temperature, the P_TME can be calculated as:

    Current sense error (0.05%) + Voltage sense error (0.05%) + 0.2% + 0.2% = 0.5%. It's important to note that this only applies over temperature. 

    This would be the expected error curve from our calculator tool which I linked earlier: 

    Best,

    Mohamed

  • 0 in reply to Mohamed Hamida
    Prodigy 100 points

    Oh wow I can't believe I didn't think about the temperature drift. Yes that lines up perfectly with the P_TME = 0.5%. We'll be operating close to 25C so I'll expect a max P_TME closer to 0.1% (and typical 0.02%). Thank you, that was very helpful.