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LM5041A: Questions about the soft start and start up

Massimiliano De Cristofaro
Expert 6640 points
Part Number: LM5041A

Hello team,

a customer of mine has the following questions about the LM5041A.

-  What is the maximum allowable capacitance for cap on pin 13 (SS)? Is 4.7uF fine or is this too much?

-  What is the max. allowed current of de-charging the capacitor through pin 13?

-  How much should be the max. current into the IC during start up?

Could you please advice?

Thank you very much in advance for your support.

 

Best Regards,

Massimiliano De Cristofaro

Central Application Engineer – Power Management

EMEA Central Application Team

Texas Instruments Deutschland

 

  • 0
    TI__Intellectual 2910 points
    Massimiliano,

    I have notified the applications team for this device of your inquiry. One of their engineers will address your customer questions within the next day.

    Regards,

    - Daniel
  • 0 in reply to Daniel Ruiz
    TI__Expert 6640 points
    Hi team,

    any news about that?

    Thank you very much.


    @Daniel: Thank you very much for your help.

    Best regards,
    Massimiliano.
  • 0 in reply to Massimiliano De Cristofaro
    TI__Prodigy 150 points

    hi Massimiliano

        Please see below answers:

    -  What is the maximum allowable capacitance for cap on pin 13 (SS)? Is 4.7uF fine or is this too much?

      A: the cap on pin13(ss) determine the soft start rate, so it's depend on the requirement of customer application. you can calculate the startup time with 4.7uF and 10uA current to see whether the cap can meet customer's requirement.

    -  What is the max. allowed current of de-charging the capacitor through pin 13?

     A: the discharging circuit is a fet inside IC, the fet will turn on when discharging, so it's discharge very fast.  The maximum value of discharge current can be measured by ampere meter.

    -  How much should be the max. current into the IC during start up?

       A: This is really depends on the startup condition, the best way is to measure input current on a certain application board. Besides, if use internal regulator and followed other test conditions on Datasheet(page 5), the maximum current during start up should be smaller than 25mA. Use external VCC and at constant condition the typical input current of IC is 3mA and maximum current is 4mA.

    Best Regards

    Tiger Tang

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  • 0 in reply to Tiger Tang
    TI__Expert 6640 points
    Hi Tiger,

    thanks a lot for your help.

    I am sending your answer to the customer.

    Thanks again.


    Best regards,
    Massimiliano.
  • 0 in reply to Tiger Tang
    Prodigy 30 points

    Hello Tiger,

    the question seems to be not clear. The discharging circuit is a FET what is turned on and discharging is very fast. That's fine. But too much current can destroy the FET. What is the maximum allowed current of de-charging the capacitor through pin 13?

    Thanks in advance.

    Best regards,

    Harald

  • 0 in reply to Harald Reichert
    TI__Prodigy 150 points
    Hi Harald
    I’m not sure the maximum current of internal FET. What I can tell you is that the discharging current is big but average current though FET is very small.
    So if you have concern about FET, there has an easy way to evaluate. Measure the maximum voltage of SS capacitor then use Q=C*V and I=Q/T to calculate average current though FET.
    Or, you can use E=0.5*C*V*V to calculate power dissipation on FET too.
    Either way, the power dissipation is very small, so I don’t think you need to warry about this. Let me know if you have further question.

    Best Regards,
    Tiger Tang