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TPS22990: Long delay time at "td"

Part Number: TPS22990
Other Parts Discussed in Thread: TPS22975

Hi

My Customer has question.

A very long delay time was confirmed on the board created by the customer
In TPS22990 DS, the delay time "td" is specified to be about 24 μs.
However, the customer's board has a delay time of about 2 ms.

TPS22990.pdf

Are there any conceivable factors?
Since customers are in a hurry, I would like you to respond as soon as possible.

Best Regard

T Kishi

  • Hi T Kishi,

    With no CT capacitance, the delay time for the TPS22990 is expected to be as low as 24us. However, the delay time scales with rise time, so if a CT capacitance is added then it will increase both delay and rise time. For example, if the rise time is increased by a factor of 10, then the delay time will also increase by a factor of 10.

    Thanks,

    Alek Kaknevicius

  • Hi Quote

    Thank you for reply.

    In the data sheet, when Ct = 0 pF, it is the following spec.(@1.05V)
    tR=12us(typ)
    tD=24us(typ)
    This time tR is about 3 ms. (250 times tR when Ct = 0 pF)
    In your opinion, I think that tD = 6 ms in customer specifications.
    However, the measurement result is about 2 ms. (About 83 times)
    Is there any other formula for checking tD?

    Regard

    T Kishi

  • Hi T. Kishi,

    The below table shows lab data on delay time vs. CT capacitance:

    CT Capacitor (pF) Delay Time (us)
    0 24
    220 28
    470 31
    1000 39
    2200 56
    4700 87
    10000 165

    Using this data, the following equation can be derived:

    Delay time (us) = 0.0139 x CT (pF) + 24.1

    Let me know if you have any questions.

    Thanks,

    Alek Kaknevicius

  • Hi Alek
    Thank you for providing data.
    The customer implements CT = 0.22 uF.
    In this case, the calculation formula is about 3 ms, but in the confirmation result it is about 2 ms.
    Is this within the error range?

    Regard
    T Kishi
  • Hi T Kishi,

    This seems to be farther off than I would expect. What is the loading condition on the output of the load switch? I have seen that a high capacitance or current load may have an effect on the delay time. The data I provided was at CL = 0.1uF and RL = 10Ω, so if your conditions are much higher than the delay time is expected to increase. For a bit more information on this, check out our timing app note:

    www.ti.com/.../SLVA883

    Thanks,

    Alek Kaknevicius

  • Hi Alek

    Thank you for information.

    Please let me ask you a question.

    Customers also use TPS22975.

    As for TPS22975 as well as TPS22990, does CT increase tD time?

    Regard

    T Kishi

  • Hi T Kishi,

    The TPS22975 behaves in the same way as the TPS22990. An increase in CT also increases tD.

    What input voltage are you looking for information for? I happen to have 1.8V and 3.3V information below (times are in microseconds):

     

     

    VIN = 1.8V

    VIN = 3.3V

    0pF

    73

    75

    220pF

    206

    215

    470pF

    316

    334

    1000pF

    509

    552

    2200pF

    965

    1088

    4700pF

    1803

    2048

    10000pF

    3976

    4531

    Using this data, the following two equations can be used to estimated tD (for CT>0pF):

    VIN=3.3V: tD = 0.438 x CT(pF) + 104.4

    VIN=1.8V: tD = 0.382 x CT(pF) + 112.2

    Thanks,

    Alek Kaknevicius

  • Hi Alek

    I am very grateful for your response.

    Can you tell us the calculation formula under the following conditions for continued recruitment in the future?

    TPS22990_22975_tDelay.xlsx


    Can you tell me the value of min / max if possible?
    (I also want such answers unless there is regulation)

    There are many, please correspond.

    Best Regard

    T Kishi

  • Hi T Kishi,

    You can expect an update on this by early next week.

    Thanks,

    Alek Kaknevicius