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LM5122-Q1: Low side FET damaged

Given Ding
Genius 10155 points
Part Number: LM5122-Q1

Tool/software:

Hi Team, 

there is low side FET damaged cased in LM5122-Q1 in boost mode. gate resistor is 0 ohm. please kindly add your comments on possible reason. 

I have asked customer to check voltage stress during start up / transient and it should be OK. 

BRs

Given 

  • 0
    TI__Mastermind 30140 points

    Hi Given,

    Could you give me more details on their design?
    The information I need would be:
    - Vin range
    - Vout
    - Max load
    - Schematic
    - inductor and MOSFET details

    Thanks and best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    TI__Genius 10155 points

    Hi Niklas, 

    Thanks for your reply.

     same sch that you reviewed before.

    inductor is PM4344332NLT. FET is buk9y6R0-60E. '

    Vin range is 9-36V, Vbat. 

     7446.sch.pdf

    BRs

    Given 

  • 0 in reply to Given Ding
    TI__Mastermind 30140 points

    Hi Given,

    Thanks for the info.
    When I was reviewing the design before, I was giving some feedback on it.
    (I do not have the previous thread at hand right now, but I assume I commented on the sense resistance of 10mOhm, which may be too small and also maybe a slightly higher inductance for general improvement. The compensation also looks non-ideal to me)

    Have these changes not been implemented?
    The schematic also confuses me here, as it uses a two MOSFET symbol (Q302), even though the seem to be using two separate Nexperia FETs.

    Could customer provide some waveforms of the switch node and output voltage of the design?
    This way we can see if the design runs unstable.

    Best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    TI__Genius 10155 points

    Hi Niklas, 

    Thanks for your reply. 

    a. why is 10mohm too small?  I do not see min requirement for Rsense. is the margin for OCP too high compared with Iout. 

    b. the sch is RTMed already for some time and bode plot has been tested.  

    c. Q302 is two FET in parallel. 

    will ask customer on the waveform you mentioned. 

    BRs

    Given 

  • 0 in reply to Given Ding
    TI__Prodigy 550 points

    Hi Given,

    Our engineer is currently out of office. Please expect a reply on Friday. Thank you.

    Best regards

    Yezi

  • 0 in reply to Given Ding
    TI__Mastermind 22720 points

    Hi Given,

    Please share some waveforms. I don't see any issue in the schematic.

    What is the part number of Q302?

    Best Regards,

    Feng