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LM46002: what will happen when LM46002 fail?

Yuan Tan63
Expert 3280 points
Part Number: LM46002

Hi,

In the Buck circuit, if an overvoltage/overcurrent/thermal problem happens and LM46002 is damaged, what the two MOSs  looks like? Short or open?  And what's the output looks like?

 

For these two MOSs, I can only find Rds-on in datasheet.

Like so many other syn Buck converters, the Rds-on-ls is lower than Rds-on-hs. However in a Buck circuit, the high-side MOS always keeps on for more than half of the cycle.  So why choose  Rds-on-ls lower than Rds-on-hs? Is this relevant with the failure model?

Thanks.

  • 0
    TI__Guru 57555 points
    Regarding you second question. When converting from 12V to 5V, for example, the duty cycle will be less than 0.5. Therefore the low side switch will be on longer than the high side. So, we design the low side with a somewhat smaller Rdson.

    Regarding your first question. Should a catastrophic event occur that would damage the power switches, they may fail either as open or short.
    Should the high side fail open, there will be no output voltage generated. Should the low side fail open, the converter may still provide an output voltage, however the switching may be erratic and/or some functionality will be lost.
    Should the high side fail short, the output voltage will reach to near Vin and other components may be damaged. Should the low side fail short, there will be on output voltage and other components may be damaged.
  • 0 in reply to Frank De Stasi
    TI__Expert 3280 points

    Hi Frank,
     Good answer, but I still confused with some points:

    1. for my first question, do you mean that the very common application for buck is D<0.5?
    2. for my second question, thanks for your complete explanation, but for " the low side fail short", is there a "no" output not a "on" output?
    3. for 2 MOSs  syn buck, the maximum voltage limitations are similar?

    Thank you.

  • 0 in reply to Yuan Tan63
    TI__Guru 57555 points
    For your 1 above; Less the most common application is D<0.5
    For your 2 above; yes I mean "no"
    For your 3 above; yes.