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TPS25947: "Itimer" of TPS25947L does not work

sugi shuichi
Prodigy 80 points
Part Number: TPS25947

(1)Could you request to confirm the circuit design of TPS25947L for 3.3V.

I have some question about the circuit for 3.3V. The condition are current "limit"= 2A, "Itimer" = 20ms. Is it OK, when the circuit of this specification the constant shown in the attached file?

Q1) Is the circuit design of "pdf" for specification(above) OK?

(2) "Latching operation" does not work
I would like to use an overcurrent protection function using "Itimer". Especially, I would like to use it instead of a fuse by "Latching Operation(Controled "Itimer")". I purchased the Evaluation Board of TPS25947 and experimented with the circuit of the attached file of (1). but it does not trip by "latching operation" at the time of overcurrent. And when the current is overcurrent, the voltage of the "Iterer" terminal does not change.

I think that It has the element in question. Short-circuit current does not flow up to the IFM current determined by the IFM resistor. This will clip the current at about 1A (50%). Therefore, when the load is short-circuited, the "Itimer" voltage (2.6V) does not start to drop, and the "latch operation" does not occur.

Q2) Please tell me the problem that the circuit of (1) does nTPS259474L.pdfot works the "latch operation".

  • 0
    Prodigy 80 points

    I send above schematic of TPS25947L for 3.3V. (I send that one by PDF. So everyone does not  see schematic)

  • 0 in reply to sugi shuichi
    TI__Guru 52770 points

    Hi Sugi,

    1. You have modified EVM as per the schematic you shared?

    2. Which channel of EVM you are testing on? What is full part number you are testing?

    3. Can you tell how are you testing? What is input voltage ? What is load type at output?

    4. First you turn TPS25947 device on and then apply load greater than 2A. How much overload you apply?

    5. Issue is that after 20ms timer is over device is not turning off?

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Prodigy 80 points

    Hi Kunal,

    Thank you for reply.
    I'm having a holiday now, So could you wait my answer until next week.

    Best Regards,
    Shuichi Sugi.

  • 0 in reply to sugi shuichi
    TI__Guru 52770 points

    Yes. No problem.

  • 0 in reply to Kunal Goel
    Prodigy 80 points

    Hi  Kunal Goel.

    I answer your questions. 

    1. You have modified EVM as per the schematic you shared?

    A)Yes, I do.

    2. Which channel of EVM you are testing on? What is full part number you are testing?

    A)CH4
       I tested full part number.

    3. Can you tell how are you testing? What is input voltage ? What is load type at output?

    A) I changed some parts value for 3.3V. Please see the last picture of the schematic.

      - input voltage :3.3V
      - A methおd of short circuit was cable using.

     - And Please see below pictures.

    4. First you turn TPS25947 device on and then apply load greater than 2A. How much overload you apply?

    A)A method of short circuit was cable using. Then I wanted to pass a current of 2A or more through the load. But TPS25947L circuit was not over 2A current. So, I think that TPS25947L is not start the "Itmer" function working.


    5. Issue is that after 20ms timer is over device is not turning off?

    A)No. Issue is not turning off. when the load is short circuit, "Itimer" of TPS25947L is not working.

    I will give you a supplementary explanation.

    Regars,

    Shuichi Sugi.

  • 0 in reply to sugi shuichi
    TI__Guru 52770 points

    Hi Shuichi,

    Device is working fine. This is correct response. During short circuit current goes above 2*current limit due to which device turns off fast and then again start limiting current to current limit. During short circuit event ITIMER is not required so it will not start to decrease. You do not see device turning off because time scale is in ms. Please keep time scale around 50us

    ITIMER only work when you apply current between ILIM and 2*ILIM.

    Please read datasheet section 8.3.5.4 Short-Circuit Protection.

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Prodigy 80 points

    Hi Kunal Goel,

     Thank you for helping a engineering of details.

     I understand your a few explanations. now I'm confirming the my questions by experiment.
    Could you wait a moment. I'll report my results.

    Thank you.

    Regards,
    Shuichi Sugi.

  • 0 in reply to sugi shuichi
    Prodigy 80 points

    Hi Kunal Goel,

    I considered below by your suggestion.

    (1) Latch by "Itimer" ; confirmed
    (2) Fast-trip latch     ; could not be confirmed
    (3) Latch in thermal shutdown  ; confirmed


    Q) Please explain detail me, what a difference between LM73100 and TPS25947.

    Proposal)
    We hope next product. please next product allow the user to set only value of "2 x ILIM", not the dependency with ILIM.

    Thank you.

    Regards,

    Shuichi sugi.

  • 0 in reply to sugi shuichi
    TI__Guru 52770 points

    Hi Shuichi,

    In all the waveforms you shared device is working as expected. What behavior you want in your application?

    Please see this file for difference between devices.

    Major difference:

    1. LM73100 does not have overcurrent protection. It does not have ITIMER so it will allow overcurrent to flow.

    2. LM73100 offers fixed short circuit protection . When current goes above 22A it will permanently latch off.

    device comparison-25947-25210-25946_user.docx

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Prodigy 80 points

    Hi Kunal Goel,

      Thank you for answering some my questions. The LM73100 has not specifications for our requests. 

    >>What behavior you want in your application?

    I expect the following behaviors. It's simply that like a "fuse" by Silicon　Chip.

     (1) When a current of 2A or more flows
         => "Itimer" is worked.

     (2) -1. After the "Itimer" operates, if a current is more 2A and more 20ms.
         => Shut off output forever

     (2) -2. After the "Itimer" operates, if a current decrease 2A during 20ms.

        => Continue to output "output voltage(3.3V)" .

    Note:

     This device has a function that makes the short circuit current constant according to the set current. We don't need this current limit feature.

    Redars,

    Shuichi sugi.

  • 0 in reply to sugi shuichi
    TI__Guru 52770 points

    Hi Shuichi,

    TPS25947 has all the features that you mentioned.

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    TI__Guru 52770 points

    Hi Shuichi,

    Closing thread now. If any other query on this topic please feel free to reply.

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Prodigy 80 points

    Hi Shuichi,

    Thank you for having supporting for me. Please close this question.
    I'll consider a few method for over current shutdown myself.

    Thank you.

    Best Regards,
    Shuichi Sugi.

  • 0 in reply to sugi shuichi
    TI__Guru 52770 points

     okay thanks.

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