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LM5010A: LM5010A

Ilan Levin
Prodigy 10 points
Part Number: LM5010A
Other Parts Discussed in Thread: LM5010

Hello,

I face a problem with the LM5010. My circuit turns it on by asserting the RON_SD to '1' after the input voltage crosses 50V. It is configured for 32V output (Data sheet resistors are set to R1=12K, R2=1K, No R3).

After the component is turned on and active for 40ms, it is shutdown by asserting the RON_SD pin to low for approx. 5ms causing the component to shutdown (this is because the input voltage drops down for a while). Refer to the attached drawing.

After 5ms the RON_SD is turned high again (and remains high forever), but still the component continues its shutdown process for approx. 150ms before it is turned on again. According to the data sheet, the shutdown time shall be approx. 1uS. 

The RON resistor is set to 100Kohm.

During first activation, there is no load (only R1 & R2). Later in the process a load is connected (by turning on a transistor). The load is connected after approx. 100ms into the shut down process.

Is that a normal behavior?

If not, what could explain such a behavior?

Thanks a lot,

Ilan

-43758598-V1-LM5010.PDF

  • 0
    TI__Genius 13735 points

    Yes, I can understand your test, it is normal, 

    Vin increase -> Vout start. -> Vin decrease ,Vout off, at thistime it have a long time for the discharge when no load connect ,

    -> next  time Vin increase, but Vout still have voltage there ,so it will wait the discharge time,

    -> Then your connect the loading, this help very fast diacharge vout, so vout goes to 0 almost, -> at this time Vin is always high, so Vout will normal start with it's soft start time.

    Final keep to normal 32V set.

    Elena

  • 0 in reply to Elena Gao
    Prodigy 10 points

    Hello Elena,

    Thanks a lot for your prompt reply and detailed explanation.

    What I still don't understand is:

    - Why does the component have to discharge after shut down? Is it indicated in the data sheet?

    - After connecting the load, I still face an even slower discharge for 45ms. Why is that? Is that the Soft start? (My Soft Start capacitor is 22nF, yielding 4.7ms soft start time).

    Thanks,

    Ilan.

  • 0 in reply to Ilan Levin
    TI__Genius 13735 points

    hi, Ilan, 

    The discharge is mostly like a Cap discharge on Vout, it's not a LM5010 feature.

    and for your soft start question ,could you send the zoom in startup waveform , and SCH  I will check .

    Elena

  • 0 in reply to Elena Gao
    Prodigy 10 points

    Hi Elena,

    I understand that the discharge is not the LM5010 feature, but why isn't the LM5010 building its output voltage right away after RON_DS is set back to  '1'.

    I'm attaching a zoom in of the diagram and the SCH.

    -43759607-V1-LM5010_ZOOM_IN.PDF-43759615-V1-LM5010_SCHEMATICS.PDF

    Thanks a lot

  • 0 in reply to Ilan Levin
    TI__Genius 13735 points

    ok, Iwill check and give you a feed back later.

  • 0 in reply to Elena Gao
    Prodigy 10 points

    Great.  I highly appreciate that. Thanks

  • 0 in reply to Ilan Levin
    TI__Genius 13735 points

    please help to check the boot voltage and waveform of boot and SW. and double check the output cap ESR is enough.

  • 0 in reply to Elena Gao
    Prodigy 10 points

    Hello Elena,

    Just want to make sure I understand.

    SW is the SW pin ?

    What do you mean by the boot voltage? 

    Do you agree that the behavior demonstrated in the waveforms I sent you is not what you would expect?

    Thanks a lot for your help,

    Ilan.

  • 0 in reply to Ilan Levin
    TI__Genius 13735 points

    hi, Ilan,

    Boot voltage means we need  to check if the HS mos is open or not, after Ron seet to 1. this is BST pin. BST should be higher than SW voltage in normal start up.

    SW is SW pin, right, it is also need to check whether it's switching or not during start up.

     Elena

  • 0 in reply to Elena Gao
    Prodigy 10 points

    Hi Elena,

    I'll do the measurements and send you the results.

    Just to make sure, can you acknowledge that the discharge in the Regulator's output is not normal after asserting '1' to RON_SD?

    Thanks a lot Elena,

    Ilan.

  • 0 in reply to Ilan Levin
    TI__Genius 13735 points

    Ilan,

    If the boos voltage is not there, then it could explain, 

    Do you have a EVM or other board or deice could try, it can help to confirm your design.

    Elena

  • 0 in reply to Elena Gao
    Prodigy 10 points

    Hello Elena,

    I was out of office and didn't monitor my mails. I apologize for not answering earlier. 

    Just want to give you a short update.

    We have added a 2 ohm resistor (R3 in the data sheet) for increasing the ESR as you recommended (previously it was 0).

    We have noticed a significant shortening in the discharge time (changed from 150ms to 50ms) , but then for some reason it returned back to square 1 (we still don't understand why).

    Another thing I have noticed s that we have a 4.7uF capacitor in parallel with the output (C884 in my schematics). Do you think it can explain the behavior?

    We have still not monitored the SW and BST pin.

    I will take your advice and order an evaluation board.

    Will keep you updated.

    Thanks a lot,

    Ilan.