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LM5141-Q1 output is very weak

user4235757
Prodigy 120 points
Other Parts Discussed in Thread: LM5141, LM5141-Q1

LM5141-Q1 5.2V.pdf

ALL ：

I am a Chinese electronic engineer，I have  problems about the LM5141-Q1，my English is very poor，so I can’t describe very detail，only with the  schematic and PCB layerout picture。

The main question:

1，  Intput Is 25V-42V，output is 5.2V

When input was 18V， load more than 200mA,it didn’t work

IC， inductance was very heat

Input was 40V,load only 20mA,it didn’t work

Oscillogram was off normal（I haven’t picture，but I am sure ）

 

2，  I am surprise that what mattered the IC heat？ As usually，the switch MOSFET is outside，main circuit current is out of the IC

 

 

  • 0
    TI__Guru 72035 points
    It would be good to see some waveforms of the SW,the HB and the gates of the MOSFETs.

    I think that your layout may need some improvement.
    The caps C4, C7, C8 need to be on the same side as the MOSFETs.
    I do not think that R4 should be there.
    The grounds for C4, C7, C8 should be close to the ground of the MOSFET.
    You should have more ground vias between the ground planes.
    It would be good to get C10 closer to the device.
  • 0 in reply to Frank De Stasi
    Prodigy 120 points

    Very thanks , I  try to change the C4 C7 C8 location as you said,this time，the load can be 1A. but the IC was too hot to be protected，so what can I solve this problem？

    and I think C10 is not  far away from the IC,even now，I can not  remoe it close to ic ,because   the path is too small。 

  • 0 in reply to Frank De Stasi
    Prodigy 120 points

    deer：

    As you said ,I change the circuit 

    Now  I change a new one  IC，it can loads 5.2V 1A(perhaps，the old IC was hurt long since),

    although ，the waves are unusual，for th epictures。 I think it case the IC be hot。But I don't know how to improve it.

  • 0 in reply to user4235757
    TI__Guru 72035 points
    The waveforms look very strange. I think that some of the layout issues should be cleaned up first.
    Adding more ground plane and attaching to the DAP of the IC will help with heatsinking.