Re: decoupling caps placement



Tim Wescott wrote:

tempus fugit wrote:

I've got a circuit that uses 3 4049 inverters. On this IC, the V+ is on
pin 8 and the ground is on pin 1. I know that the decoupling caps need
to be as close to the IC as possible, but how can I connect 1 end of the
cap to V+ and the other to ground when the pins are so far away? Is it
sufficient to connect 1 end of the cap to V+ and the other to a nearby
ground node, or should the cap be connected close to the actual ground
pin of the IC? Also, do I use 1 cap for each IC? If so, (the ICs are
fairly close together) wouldn't the IC "see" the caps as being the
paralleled value of the 3 caps, thus reducing the available capacitance?
I was going to use 0.1uF for the value of each decoupling cap. Would it
also be wise to use a larger (1uF or higher) cap in parallel?

For that chip a 100nF (0.1u) ceramic up by pin 1, with a lead straight to
pin 1 and another one straight to pin 8 will be more than sufficient.

You can think about reducing them later -- but why? Unless you're trying
to shave deci-pennies off of the board cost, it's better to have too many
bypass caps than just enough.

Heck, I don't even always bother with one decoupling cap per chip with HC
logic !

Now consider a 40MHz '8051' with the power on pins 20 and 40 !

Graham

.

Relevant Pages

  • Re: decoupling caps placement
    ... I've got a circuit that uses 3 4049 inverters. ... and the ground is on pin 1. ... close to the IC as possible, but how can I connect 1 end of the cap to V+ ... case you would put the cap next to the positive power pin and then to ...
    (sci.electronics.basics)
  • Re: decoupling caps placement
    ... I've got a circuit that uses 3 4049 inverters. ... pin 8 and the ground is on pin 1. ... sufficient to connect 1 end of the cap to V+ and the other to a nearby ... (low level audio is an exceptional ...
    (sci.electronics.basics)
  • Re: info needed for 6L6GC tube voltage or shematic for old TUSC guitar head
    ... BTW a short from pin 4 to 5 is something I have never ... the cap at the ground switch and the PE connection would be illegal. ... the proper instalation of a 3-prong cord. ...
    (alt.guitar.amps)
  • Re: Gottlieb problems
    ... If you are paranoid about soldering on the CPU board, ... the reset is also connected to connector P7 pin 1 (unused, ... So female .093" Molex connector pins can be soldered directly ... cap leads. ...
    (rec.games.pinball)
  • Re: Bright flashing light for fake alarm box?
    ... I think you left out the pin numbers so I put Pin One in. ... > Rt 470k ohms ... You can adjust the frequency of flashes by changing Rt or Ct. ... but it'll be hard to get a 10uF cap that is low leakage. ...
    (sci.electronics.basics)