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TPS54340: TPS54340 question about countermeasures against surge current.

Bob Lee62837
Mastermind 7230 points
Part Number: TPS54340
Other Parts Discussed in Thread: TPS54341

Dear support member,

My customer used TPS54340.

I have a question.


(Question)

Q1
We are considering countermeasures against surge current after TPS54340.
A surge of 30 to 35 A / 800 u to 1 ms occurs as a triangle wave at the rear stage of DCDC.

Is it the output response within range of DCDC?
Does the output voltage drop significantly?

Q2
If the response of Q1 is in time, Does overcurrent protection work?
If there is information such as "There is no problem because overcurrent has ** ms delay"
Could you teach?

Q3
In case Q1 does not make the response over range of DCDC or Q2 takes overcurrent protection,
We believe that there is no other choice but to cope with increasing the capacitor capacity of the DCDC output,
but if you include the tolerance and margin for calculation, it will be required about 4000uF.

Is it OK to increase the DCDC output capacitor so much?


Q4
In case of countermeasures against surge with capacitor capacity increase of DCDC output Since it usually thinks it is about several tens of uF and the start time is about 2 to 5 ms
I think it will take 500 ms to 1 s if 4000 uF.
Does it correct?

Best regard.

Bob Lee.

  • 0
    TI__Genius 11040 points
    Hi Bob,

    The product expert will follow up with you on your questions.

    Best Regards,
    Katelyn
  • 0 in reply to Katelyn Wiggenhorn
    TI__Expert 6215 points
    Hello Bob,

    The TPS54340 has cycle by cycle current limiting. Current will be limited to approximately 5 A. While a load greater than this value is applied, the difference must be made up by the converter’s output capacitors. If the output voltage falls below zero the catch diode supplies current.

    1) The answer to Q1 depends on the value of the output capacitor since when output current is greater than 6 A, the capacitor’s value determine the rate at which output voltage falls. See answers to Q3 and Q4 for 2 mF.

    2) Q2, Current is sensed every cycle so current limited very quickly. When the load is removed, output voltage recovers.

    3) We usually recommend that a device with adjustable soft start such as the TPS54341. Also, most large capacitors have larger than expected ESR so include ESR when calculating compensation.

    4) To calculate the answer to Q4, assume that output current during startup is 2 A.

    Regards, Robert
  • 0 in reply to Robert Blattner
    Mastermind 7230 points

    Dear Robert,


    Thank you very much for reply.
    I reply my customer your answer.

    I will feed back it.


    Best regard.
    Bob Lee.