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P-Channel MOSFET Load Switch w/ Soft-Start

I am making a board that will have 3 high-side P-Channel MOSFETs used a load switches to 3 different loads. They will switch on/off 12V,

24V, and 36V battery packs. They need to have soft-start on-switching (and fast off-switching). Load currents will be 1-10Amps. They will be controlled by PIC outputs. I don't know much about using MOSFETs. Is there such a thing as a P-Channel MOSFET driver with soft- start that will work in the 12-36V range? I have seen a couple parts that would be perfect but they're for low voltage supplies like 5V. Or if I made my own driver with discrete parts, I'm not sure how to do it. It needs to be small, I was hoping to do it with an SOT-23-5 sized part. Can anyone help? Thanks.
Reply to
jackm.saic
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How soft? How fast?

John

Reply to
John Larkin

Soft-start ON rise time would be nice to have it be a few milliseconds, or adjustable by a 1206 capacitor. As for switch-OFF time, I don't really have an answer. From reading datasheets of other MOSFET drivers, I have seen fast OFF times as being a feature of the drivers, so I assumed that meant fast OFF switching time was good thing to have. This design will be for a generic battery pack controller board that will potentially be powering several different types of electronic loads. An example of a part I'm looking for would be similar to the Fairchild Semi FDG901D. This part would be perfect but it only works to 6V.

Reply to
jackm.saic

P Channel FETs in the supply are controller by an NPN on the GND. Meaning have a pullup on the gate of 20k or so, and have an NPN with an emitter resistor on GND forming a current sink. The base can be connected to the logic.

Choose the emitter resistor such that sufficient current flows while the voltage on the gate doesn't exceed 10V or so.

Speed is an issue for the resistor values.

Rene

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Reply to
Rene Tschaggelar

What is the advantage of using an NPN as the P MOSFET controller instead of using a small signal logic-level N MOSFET to control it??

Reply to
jackm.saic

You could did that too!

Reply to
Mook Johnson

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