[SI-LIST] subscribe: bypass capacitor
- From: "Zhao Yu" <tianfeiyu@xxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 26 Jan 2005 23:09:12 -0600
dear sir,
I confuse to use the bulk bypass capacitor. It is sai= d that the bulk
capacitor is not to cancel the switch noise,but to eliminat= e the low
frequency noise such as refresh of DRAMs. So i think it does not = need to
place the bulk capacitor near power pins of chips, Is it right?(que= stion
1)
And i see some mater= ials which recommed to place lots of small
distributed bulk capacitor on th= e board instead of using a few large bulk
ones. So if this idea is true, wh= en we choose the bulk capacitor,we only
need to calculate all the current i= n the circuit and choose the
corresponding bulk capacitors whose sum is equ= al to the request, then
distribute them on the board. That is to say we nee= d not to choose bulk
capacitors according to precise requirement of every c= hips and assign
everychips a bulk capacitor.Is that right?(question 2)
= At very low frequecy, up to seve= ral KHZ typically, the voltage
regulator module supplies enough low impedan= ce and the ripple voltage is
small enough. So we need no bypass capacitors = in this bandwidth. Compared
with a actual system, i concider the power chip= s as the voltage regulator
module, but as we know the power supply circuit = contain a large value
capacitor used to keep stable voltage, can i concider= it as a bulk
capacitorand subtract its value from the requested bulk capa= citance by all
the circuit? (question 3)
&= nbsp;
BEST WISHES
--=20
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