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LMP8601-Q1: midscale offset issue

Bernhard Lieb
Prodigy 30 points
Part Number: LMP8601-Q1
Other Parts Discussed in Thread: LMP8601, INA240-Q1

Hi, I have questions regarding LMP8601-Q1

1) What does this value "midscale offset scaling accuracy" stand for? What does it mean?

2) What is the meaning of the absolute value "Input referred"?

3) The value under chapter 6.7 (SNOSAR2H –SEPTEMBER 2008–REVISED APRIL 2016) says that the OFFSET pin is grounded. So while measuring low currents, do I still have negative tolerances as well?

4) Does there a dependence between output voltage and midscale offset scaling accuracy?

Thank you.

Kind regards.

  • 0
    TI__Intellectual 1235 points

    Hi Bernhard,

    Bernhard Lieb said:

    1) What does this value "midscale offset scaling accuracy" stand for? What does it mean?

    2) What is the meaning of the absolute value "Input referred"?

    The midscale offset scaling accuracy is the offset error generated when setting OFFSET > 0V. The 6.7 specification is tested at Vs=5V, so it is the offset error when OFFSET=Vs, thus Vbias = 2.5V. For example, when LMP8601 is set to midscale offset (OFFSET=Vs), there will be 0.625mV offset (referred to input, RTI) generated. You refer this error to output by multiplying by total gain (20V/V), which is 0.625*20 = 12.5mV. This results in a relative error of 12.5mV/2.5V = 0.5%

    Bernhard Lieb said:
    3) The value under chapter 6.7 (SNOSAR2H –SEPTEMBER 2008–REVISED APRIL 2016) says that the OFFSET pin is grounded. So while measuring low currents, do I still have negative tolerances as well?

    Midscale offset scaling accuracy is only applicable when OFFSET > 0V, so the midscale offset scaling accuracy error is 0% when OFFSET is grounded.

    As a side note, INA240-Q1 is a newer alternative with better accuracy and lower cost compared to the LMP8601-Q1. It also has an enhanced PWM rejection feature. I recommend you check it out if negative common-mode of -4V will suffice. 

    Thanks,

    Cierra