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Original question:

LM5069 - pulling GATE pin to GND for fast turn-off

LM5069: LM5069 - fast turn-off circuit

Jessica Riley90
Prodigy 180 points
Part Number: LM5069
Other Parts Discussed in Thread: TPS2490,

Hello,

I was reading the TI app note SLUA500 which shows a fast external turn-off circuit using the TPS2490 hotswap controller. 

The recommended circuit for increasing turn-off speed in the LM5069 datasheet when using dv/dt slew rate for slow turn-on only removes the extra external capacitor; the turn-off speed is still limited to the current sink capability of the IC (which is pretty weak).  The advantage of the circuit above for the TPS2490 is it uses the external transistor path to provide a stronger turn-off current than the IC can provide. 

So my question is: is there any issue implementing the faster turn-off circuit from the TPS2490 app sheet with the LM5069 hotswap controller?  I've simulated it and it appears to function as I would expect (slow turn-on, fast turn-off), but I want to make sure there are no gotchas before proceeding down this path.

Thank you,

Jessica

  • 0
    TI__Guru** 103766 points
    Hi Jessica,

    There is no harm in following the same approach even with LM5069, however I didn't see as a must need. The pull down strength for LM5069 is good enough to discharge the external FET gate capacitance for decent turn-OFF speed. The extreme fast turn-OFF will have adverse effect (Vin bounce back) if there is any source inductance at the input.

    Best Regards,
    Rakesh