[SI-LIST] Re: Using Load Switching FETs

Jim,

   How fast are you trying to switch the loads ? The classic trade off
between on resistance is capacitance. The Cap load tends to be sizeable. 

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Jim Hall
Sent: Monday, March 26, 2007 1:28 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Using Load Switching FETs


Hello,

Does anyone have any thoughts on using load switching FETs between a main
power plane and a local power plane devoted to 1 or 2 ICs?

Some of the PFETs offered these days feature Rds values below .01 ohm and
package para- sitic inductances of a nH or so. For situations where one has
many ICs with multiple voltage supplies that have to be sequenced on in a
particular order, the FETs seem very attractive. I realize that for fast ICs
with large dI/dt needs, the parasitic L could be a bottle neck. But can this
not be compensated for with a properly chosen array of de- coupling caps,
and would the same issue not exist for point of load regulator modules?

Any advice would be appreciated.

Thanks,
Jim

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