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LP5569: PWM output formulas in data sheet 09/2017 look to be wrong

Luca Matteini
Prodigy 20 points
Part Number: LP5569

On september 2017 data sheet pages 13-14 I read these formulas:

Assuming the graph is correct (and that makes sense), with a very quick approximation seems to be resulting from:

x <= 64:  y  = 0.0245 * x

x > 65:  y = 0.3886 * exp( 0.0217 * x )

Supposed I'm not wrong, that "0.0217" is the only valid constant mentioned in the datasheet(...).

Can anyone confirm/verify this?

Thanks

  • 0
    TI__Intellectual 950 points
    Luca,
    Please use the equation described in the datasheet to calculate PWM output. The figure may have some errors.
    Thanks,
    BRs,
    Rosley
  • 0 in reply to Rosley Ge
    Prodigy 20 points

    Rosley,

    this is the graph plotted from the equations in the datasheet:

    the step at transition from code 64 to code 65 is quite awful, such that would appear as the light (almost) blinking, instead of fading.

    Moreover, at code 255 the resulting PWM percentage would be around 198%, which is not possible (unless codes higher than 223 just mean 100%, hence being useless).

    Here's why I supposed the formulas to be unrealistic, while the graph in data sheet is very possible.

    Luca

  • 0 in reply to Luca Matteini
    TI__Intellectual 950 points
    Luca,
    I understand your concern but please follow the equation in the datasheet for the calculation. It is something from design team. It should be most accurate.
    Thanks,
    BRs,
    Rosley