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LTC4417 Gate falling to slow before switchover

Hi there

I use the LTC4417 in following application:

  • On V1: 12V from PoE
  • On V2: 9-30V DC-Input
  • On V3: 9-30V DC-Input

I have the following problem, when switching from V3 with 30V to V2 with 9V:

  • The gate voltage of transistor at G2 (after inrush-limiting-circuit) is not falling the same rate as VOUT and hence, at switchover the G2 has to discharge quiet a lot.

Following chart shows the details.

Legend:

  • Yellow: V2 (9V is connected)
  • Green: VS2 (source-voltage)
  • Purple: Gate of P-Channel-Transistors
  • Blue: VOUT

Until the switchover happens, the gate- & source-voltage only falls by 7V volts. And with the inrush-limiting-circuit the switch-over time takes too long, so that VOUT droops too much.

I have already checked the Inrush-current, but I can't increase it further more.

If have tested quiet a lot and by increasing CS2 to 100nF the source and gate voltages are falling faster. But then I am not meeting the recommendation of Setting CVS ten times CS

The same problem occurs also if changing from V2 on 30V and V3 on 9V, when disconnecting V2.

My questions are:

  • Is there a way to increase the fall rate of gate- & source-voltage?
  • Is it really necessary that CVS ten times CS?
  • Or is it just too ambitious to have the LTC4417 working with 9V and 30V input supplies?

Appreciate your answers!

Kind regards, Chris

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