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MC33063 Accuracy of output

Tomoaki Yoshida
Expert 2200 points

Hi,

We are going to use the MC33063 as an inverting regulator.

Then Vout is -5V for negative rail of opamp.

Variations of the comparator threshold is ±3.2% over the full range.

Can I think that the accuracy of output is ± 3.2% full range?

I would like to know output drift.

Is there any information of temperature drift?

best regards,

Tomoaki Yoshida

  • 0
    TI__Mastermind 24975 points
    Hello Yoshida-san,

    The variation of the threshold voltage is not going to be +-3.2% over the full range for a given device, it is going to be better. This variation over the full temperature range also considers the offset variation at 25C. For example, some devices will have a typical threshold voltage of 1.275V. These devices still will not exceed the 1.29V over the full range of temperature, suggesting that the variance over temperature is less than 3.2%. It is likely more on the order of 1.2 to 1.3% [ (1.225 - 1.21)/1.21 or 1.29-1.275/1.275 ].
    Unfortunately I don't have any specific data for temperature drift, but the datasheet suggests that 2% variation (or better) over temperature (relative to 25C) is very reasonable to expect.

    In short, you could have a +-3.2% worst case variation across devices, but for a given device over temperature the drift is going to be better.
    Does that make sense?

    As you mentioned the accuracy will depend on the accuracy of the internal reference. Additionally it will depend on the accuracy of R2 and R1 which could cause drift to be worse over temperature.

    Best,
    Michael
  • 0 in reply to Michael J Schultis
    Expert 2200 points

    Hi Michael,

    Thank you for your reply.

    I could understand the accuracy and drift of comparator.

    As you said, the accuracy of the output is also dependent on the internal reference.

    It seems there is no description in the electrical characteristics for the accuracy of the internal reference, do you have any information about the internal reference?

    Can I think that the accuracy of the output is +-3.2% worst case included internal reference?

    best regards,

    Tomoaki Yoshida

  • 0 in reply to Tomoaki Yoshida
    TI__Mastermind 24975 points
    Yoshida-san,

    Yes, the threshold voltage is based on the internal reference.
    Absolute worst case scenario for accuracy would be +-3.2% as stated in the datasheet. I don't expect it to ever be that bad though.

    Best,
    MIchael