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TPS3808: Output Capacitance and Capacitive Loading

Richard Elmquist
Mastermind 45250 points
Part Number: TPS3808

Do we have any information on the output capacitance of the SENSE pin?

There is nothing in the data sheet that defines the capacitive load that the SENSE pin can drive. Do we have any information on this?

Thanks for your help with this!

Richard Elmquist

  • 0
    TI__Genius 12630 points

    Richard,

    "Output capacitance of the SENSE pin" confuses me. The SENSE pin is an Input pin, not an output. The input capacitance of any input pin is spec'd at 5pF in the EC table. This also includes the SENSE input pin.

    I am not sure if this answers your question but please let me know.

    -Michael

  • 0 in reply to Michael_DeSando
    TI__Mastermind 45250 points

    Michael,

    My mistake! I meant the reset pin.

    My customer is really wanting to know the output capacitance of the pin. He also asked about the drive capabilities of this pin, but I tried to explain that this is an open drain. This would be defined by the pull-up resistor and voltage.

    Thanks for your help with this!

    Richard Elmquist

  • 0 in reply to Richard Elmquist
    TI__Genius 12630 points
    Richard,

    Although we do not provide the output capacitance value, we do provide the recommended drive capabilities in the Recommended Operating Conditions in table 7.3. Here you will find the recommended max voltage and current for /RESET pin which is set by the pull-up resistor and pull-up supply voltage as you had mentioned. Also, by knowing the pull-up supply voltage and the pull-up resistor value, you can calculate the /RESET pin current. Using the /RESET pin current and knowing the pull-up supply voltage, you can estimate the output capacitance using:

    I = C * dv/dt

    where I: /RESET pin current, C: capacitance, dv: change in voltage on /RESET pin (0V to pull-up supply voltage), dt: propagation delay (found in Switching Characteristics Table 7.6). If you use the actual propagation delay value measured then the capacitor estimate will be more accurate. You can use typical prop delay of 20us.

    I calculated a rough estimate of the output capacitance to be ~15nF.

    Please let me know if this answers the Customer's question or if any additional support is needed.

    -Michael
  • 0 in reply to Michael_DeSando
    TI__Mastermind 45250 points

    Michael,

    Thanks for your quick response!

    I will let you know if the customer has any further questions.

    Have a great day!

    Richard Elmquist