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TPS22976: About normal distribution date of TPS22976

Yurie.H
Intellectual 320 points
Part Number: TPS22976


Hello.
Our customer is considering to use the following TPS22976.
Therefore our customer want to normal distribution date of turn on time.
Do you have this date?
Best Regards
Yurie
  • 0
    TI__Genius 10855 points

    Hi Yurie, 

    Thanks for reaching out on E2E!

    Unfortunately, the timing of the TPS22976 is ultimately dependent on operating conditions and external components around the load switch. Depending on the output load resistance, bias voltage, and your input voltage, the rise time of the switch can vary.

    You can approximate the rise time of the TPS22976 by using the slew rate equation on page 22 of the TPS22976 datasheet. After finding the slew rate, you can calculate the trise time with this approximate equation: trise = Vout * SR * 0.8

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Intellectual 320 points
    Hi Arthur,

    Thank you for the reply.

    Please tell me about the ceremony you taught. (trise = Vout * SR * 0.8)

    What is the accuracy of this formula after removing the variation of the capacitor?
    The accuracy does not deviate by ± 50%, is not it?

    Best Regards

    Yurie
  • 0 in reply to Yurie.H
    TI__Genius 10855 points

    Hi Yurie, 

    This formula (trise = Vout * SR * 0.8)  is dependent on the accuracy of calculating the slew rate, SR. If you look at page 8 of our app note, Basics of Load Switches, you can see that we use the same (trise = Vout * SR * 0.8) equation across all our load switches. Therefore, the accuracy is dependent on the value you determine for slew rate.

    To calculate the slew rate, I recommend using the equation on page 22 of the TPS22976 datasheet, as mentioned above. The accuracy will not deviate by ± 50%, we found the equation by taking multiple data points across multiple devices in our characterization data.

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Intellectual 320 points
    Hi Arthur,

    Thank you for the reply.

    On page 22 of the TPS22976 datasheet, there is a SR(slew rate) expression, not a trise(trise = Vout * SR * 0.8) expression.
    trise = sr * Vin : Does it match?
    trise = Vin * 0.42 * CT + 66 : Does it match?
    Is the expression "trise = Vout * SR * 0.8" and "trise = Vin × 0.42 × CT + 66" together?
    In that case, what numbers are 0.42 and 66?

    And Is there a document on accuracy of this device?

    Best Regards,

    Yurie
  • 0 in reply to Yurie.H
    TI__Genius 10855 points

    Hi Yurie, 

    The expressions/equations can't be combined, slew rate is the rate at which the output rail ramps up to the input rail when the device turns on. Trise is the time the output rail takes to go from 10% to 90% of the input rail.

    Since trise is calculated as the time from 10-90%, this is where the trise = SR * VOUT * 0.8 comes from. Therefore, here are the steps I would follow: 

    1. SR = 0.42 * CT + 66
    2. trise = SR * VOUT * 0.8

    The 0.42 and 66 values are calculated after collecting characterization data from the device. After we collect trise information in various scenarios, we approximate the SR with this equation. The equation won't be the exact value from your system, but it will provide a good approximation. 

    The best way to calculate the exact turn-on time of the device is to get an evaluation module of the TPS22976 and calculate the turn-on time. Note that the value can be different than the datasheet value if the load resistance, input current, or load resistance are different.

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Intellectual 320 points
    Hi Arthur,

    Thank you for your kindness.
    I understand.

    Best Regards

    Yurie