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TPS54318 PH pin maximum ratings

Other Parts Discussed in Thread: TPS54318

TPS54318 PH pin voltage over maximum ratings at switching dead time.

The dead time was about 20ns.

Maximum ratings are the following.

-PH: -0.6 to 7V

-PH 10ns transient: -2V to 7V

I tested with EVM.

Test condition was 5Vin, 1.8Vout, 3Aout.

PH pin voltage fall below -0.6V for about 20ns.

Is there possibility that the device is broken by this?

3365.Fall down waveform.TIF

2148.Rise up waveform.TIF

  • We get this issue a lot.  The -0.6 V rating is from the process specification.  It is a long term dc value.  Obviously for switching power supply, that is not a realistic condition.  So we created the included transient spec of -2 V for 10 nsec.  That spec is somewhat arbitrary, and in most cases is driven by a previous customer complaint.  So if they saw -2 V for 10 nsec, that is what we would test to.  So of course there is always some variation as well as differences in measuring technique.  Also there is the inductance of the bond wires to consider.  The negative excursion at the die will almost certainly be less than you show.  In my opinion, that waveform looks acceptable, but it is only my opinion.  TI would have to re-test to a higher spec time and duration to guarantee it. 

  • My customer requires the guarantee that TPS54318 isn't destroyed by this waveform.

    If it is possible, how long time does it take?

    If it isn't possible, could you give me the data how much level is the negative voltage relieved by inductance of the bond?

     

  • I do not directly support that device.  I just have a general knowledge of this topic as it pertains to the TPS54xxx line of switch converters.  From my personal experience, -3 V is the threshold for issues.  Usually it is not destructive, but may cause the device to latch off or have internal false fault conditions.  I'll pass this along to the proper business unit.