• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 63 subscribers
  • Views 726 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS92692-Q1: Internal PWM generator Accuracy

Ryuji
Guru 20090 points
Part Number: TPS92692-Q1

Hello,

In the datasheet page 9, the PWM duty cycle equation is the following.

DPWM(INT) = (VDIM-1) / 2

When considering the accuracy of duty, is it enough to consider the accuracy of VDIM?
Is there a variation in "-1" and "2" in this calculation formula?

Best Regards,
Ryuji

  • 0
    TI__Mastermind 25500 points

    Hello Ryuji,

    It will mostly depend on the accuracy of VDIM, but you are correct that there will be some dependence on "-1" and "2" in the equation. That is actually related to the tolerance of the 1V and 3V thresholds of the ramp generator. I can't give any guarantee on the tolerance of those since the min/max isn't specified in the datasheet. But I will ask the IC designer for a realistic tolerance in those voltages and let you know. But some variance in those would result in very little variance of the duty cycle.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Guru 20090 points
    Hello Clint san,

    Thank you for the reply.
    I'm waiting for information.

    Best Regards,
    Ryuji
  • 0 in reply to Ryuji
    TI__Mastermind 25500 points

    Hello Ryuji-san,

    Again none of this can be guaranteed since it is not production tested, but the variation on the 1V and 3V thresholds is +/-4%. They both track in the same direction with any variation which is good. Not including the tolerance of the control voltage this roughly translates to a duty cycle variation of about 1% at 90% duty cycle, about 2% at 50% duty cycle, and a little over 20% at 4% duty cycle. That small variation translates to larger error as the duty cycle decreases since it becomes a larger portion of the overall on time.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Guru 20090 points
    Hello Clint san,

    Thank you for the information.
    How did you calculate the accuracy of PWM (about 1% at 90% duty cycle , about 2% at 50% duty cycle)?
    The same result was not obtained , when I calculated with ± 4% accuracy to "1" and "2" of DPWM (INT) = (VDIM - 1) / 2 in the calculation formulas of the data sheet.

    Best Regards,
    Ryuji
  • 0 in reply to Ryuji
    TI__Mastermind 25500 points

    Hello Ryuji-san,

    That isn't from a calculation. Those numbers are just estimates the IC designer made based on his simulations.

    Regards,

    Clint