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TPS22810: The maximum value of Ct and the rise time when it is greater than 27000pF

Shinichi Inoue
Guru 21626 points
Part Number: TPS22810

Tool/software:

Dear Specialists,

My customer is considering TPS22810 and has question.

I would be grateful if you could advise.

---

(1)Is it possible to use a capacitor value (27000pF) greater than that listed in "Table 2. Rise Time Table"?

What is the maximum value of Ct?

(2)Could you please let us know the table or formula for values ​​greater than 27000pF.

---

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Mastermind 28180 points

    Hi Shinichi-san,

    1. Yes, there is no maximum value of CT. However, if there is a large load current while the device is charging, it may go into thermal shutdown because of the large power dissipation (large current across high Ron), but this is unlikely unless using a constant current load.

    2. The formula to estimate the rise time/slew rate would be the same as what is in the data sheet.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Guru 21626 points

    Hi Patrick,

    Thank you for your reply.

    Actually the customer wants to use the TPS22810 with a 5V power supply inrush current of 6A/20ms.

    Is TPS22810 possible to use?

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    Guru 21626 points

    Hi Patrick,

    The customer has an additional question.

    Could you please advise?

    ---

    When calculating using the formula in 9.3.4 Adjustable Rise Time (CT), the result is different from the result in Table 2. Rise Time Table.

    Is there a problem with the formula?

    When VIN=5V, Ct=470pF

    SR = 46.62 / 470pF = 0.0992V/us

    RISE TIME (µs) 10% - 90% is the regulation, so 5V x 0.8 = 4V

    Rise Time = 4V / 0.0992V/us = 40.3us

    In Table 2. Rise Time Table, the result is 63us, which is about 20us off.

    ---

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    Guru 21626 points

    Hi Partrick,

    This is just a reminder.

    I'm looking forward to waiting your suggestion regarding an additional question listed above.

    I appreciate your great help.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    Guru 21626 points

    Hi Patrick,

    I'm still looking forward to waiting your reply.

    The customer wants to obtain about additional questions.

    ---

    When calculating using the formula in 9.3.4 Adjustable Rise Time (CT), the result is different from the result in Table 2. Rise Time Table.

    Is there a problem with the formula?

    When VIN=5V, Ct=470pF

    SR = 46.62 / 470pF = 0.0992V/us

    RISE TIME (µs) 10% - 90% is the regulation, so 5V x 0.8 = 4V

    Rise Time = 4V / 0.0992V/us = 40.3us

    In Table 2. Rise Time Table, the result is 63us, which is about 20us off.

    ---

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • +1 in reply to Shinichi Inoue
    TI__Mastermind 28180 points

    Hi Shinichi-san,

    The values in Table 2 and in the Electrical Characteristics table are tested on silicon, whereas the equation is for estimating the rise time for CT values which are not listed in the table. If the customer is using one of the CT values listed in the table, please use that number, and if they are not, please use the equation and validate the performance before the system goes into production.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Guru 21626 points

    Hi Patrick,

    Thank you for your reply.

    I've been waiting for the answer.

    I shared your answer with the customer.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi