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TPS28255 FET driver not enabling at start-up

Zeeshawn Shameem
Prodigy 10 points
Other Parts Discussed in Thread: TPS28225

Hello,

I'm using the TPS28255 to drive a half-bridge (HB).  I tie the EN pin to VCC, so it starts up at same time as VCC.  When duty cycle is high (>90%), the HB intermittently gets stuck (no switching).  If I disable and enable, it works fine.  I found if I delay the enable signal, the TPS28255 never sees this issue.   

The datasheet doesn't mention sequencing of EN pin vs VCC... in fact, the simplified schematic on page 1 shows EN pin tied to VCC.  Is this an issue?  

Thanks,

Zeeshawn

  • 0
    TI__Expert 3200 points
    Zeeshawn,

    I will forward your question to a knowledgeable AE.
  • 0
    TI__Intellectual 1875 points
    Hi Zeeshawn,
    I believe you are using TPS28225. Correct?
    Assuming you are asking about TPS28225, I do not believe there is any sequencing requirement.
    It might be possible that the driver might be entering either the tri-state mode or thermal shutdown mode.
    It is also possible that the noise on any of the pins might be causing this behavior.
    We have seen driver performing intermittently when one or more of the inputs are operating very close to thresholds.
    Sometimes unusual slew rate might also cause driver output to be non-compliant.
    It is surprising that by delaying EN pin, the phenomenon disappears.
    How are you delaying the enable. Have you pulled the enable through a resistor?
    How long does it take for the driver to get stuck into shut-off mode (both outputs off)?
    How long does it stay in that mode? Does it recover by itself (do not do anything with circuit)?
    May I have schematic, waveforms, and parameter details from you to further help you?

    Thanks and regards,
    Ritesh