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LM20: Question on unit of measure for line regulation

Carl Ballard
Prodigy 50 points
Part Number: LM20

Hello.

We are working with the LM20BIM7 part.

I have a question about the units for line regulation.

The first line regulation test lists the test conditions as 2.4V≤V+≤5.0V, with the maximum limit of 3.7 mV/V.

The second line regulation test lists the test conditions as 5.0V≤V+≤5.5V, with the maximum limit of 11 mV.

Can you please explain why the first test specifies the limit in mV/V, and the second test specifies the limit in mV?

Shouldn't both tests list the same unit of measure?

Thank you.

  • 0
    TI__Genius 12165 points

    HI Carl,

    I don't know if its a typo, but yes ideally they should have the same unit to avoid confusion, I wish it was clearer. 11mV of line regulation in that range means that the maximum change in the output voltage from +5V supply to +5.5V supply is 11mV. If you would prefer the mV/V units, that means it becomes 22mV/V (11mV/(5.5V-5V) = 11mV/(0.5V) = 22mV/V). 

    Regards

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 50 points

    Hi Alex.

    This does help somewhat.

    If we were to specify the units as mV, then the limit for the test condition 2.4V <= V+ <= 5.5V would be 3.3 mV/V (5.0-2.4V) = 3.3mv/V (2.6V) = 8.58 mV.

    Is this correct?

    Thank you

    Carl

  • 0 in reply to Carl Ballard
    TI__Genius 12165 points

    Carl,

    Yes this is correct.

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 50 points

    Hi Alex.

    We are going to be testing this LM20.

    Can you please provide the test methodology to test for line regulation, both at test conditions 2.4V <= V+ <= 5.0V and 5.0V <= V+ <= 5.5V?

    Thank you.

  • 0 in reply to Carl Ballard
    TI__Genius 12165 points

    Carl,

    To determine line regulation, we measure the LM20 against a calibrated reference and sweep temperature in a controlled environment, and read the analog output to get the temperature error. At each temperature, supply voltage is stepped, in this case at least 3 supply voltages were tested per temperature (2.4V, 5V, 5.5V). The line regulation is calculated in post-processing. The analog output of the part at a given temperature will change with different supply voltages, so the change in the analog output between 2 supply voltages is divided by the change in voltage supply. If you only want evaluate the line regulation at room temp, just measure the analog output at multiple different supply voltages, and apply the equation: LR = (Vout_A - Vout_B)/(VDD_A - VDD_B)

    Regards

    -Alex

  • 0 in reply to Alex Thompson
    Prodigy 50 points

    Alex, this is great information. If we wanted to test this at temperatures other than room temp, we'd just have to stabilize the temperature of the part and perform this same type of measurements. Thank you.