[SI-LIST] Re: Placement of decoupling capacitors
- From: Khalid Ansari <khalida@xxxxxxxxxxx>
- To: Larry Miller <lmiller@xxxxxxxxxxxxxxxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Tue, 31 Jul 2001 14:10:33 -0700
Larry,
>I think you have it right on placing the smallest caps (highest frequency)
>closest to the pins, but these are very small (we use 0603's), so the next
I just have enough space to place this one close to the pin, the rest have
to go quite further away due to space constraint. Placing them too far
away I have to worry about the loop inductance.
Are there any issues with piggy backing capacitors?
>bigger (lower frequency) ones are not that much further away. By the time
>you get to the bulk caps, they only have to be in the general neighborhood.
>
>No tricks or piggybacks needed-- the lower the frequency range you need to
>cover the less critical the placement. This is especially true where you
>have power and ground planes that are essentially zero ohms at lower
>frequencies.
>
>My opinion, anyway, and we haven't had any problems following this idea.
>
>Larry Miller
>
>-----Original Message-----
>From: Khalid Ansari [mailto:khalida@xxxxxxxxxxx]
>Sent: Monday, July 30, 2001 2:19 PM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Placement of decoupling capacitors
>
>
>
>I looked through various emails from Larry Miller, Larry Smith and the rest
>who had contributed to a discussion earlier on decoupling. Those
>emails helped me select the values for decoupling caps but now the
>challenge is, how do I place these? I don't have enough room on each of my
>power supply pins to place these caps around. If I try to place the
>cap that decouples the highest frequency components out of the selected
>ones close to the power pin and the one that decouples the lowest frequency
>components the farthest, the caps are being placed too far away from the
>pin.
>Can I piggy back these caps? What are some of the tricks to overcome this
>problem?
>
>Thanks in advance,
>
>Khalid
>
>
>
>
>
>
>
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