[SI-LIST] Re: VOH datasheet question
- From: "Robert Sefton" <rsefton@xxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 9 Mar 2006 12:56:10 -0800
Chris -
VOH is a DC parameter and should be in the DC parameters section of the data
sheet. Capacitive loading affects the AC performance, i.e., tPD, rise/fall
times, etc. The AC performance is definitely related to the DC drive
capability, but you have to do the AC analysis separately.
Bob S.
---------------------------------------------------
From: "Chris Chalmers" <cchalmers@xxxxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Si List,
This is a bit of a basic question, I just need a push in the right =
direction.
In datasheets for a CMOS buffer running from 3V, the VOH min=A0 is = stated
as=20 2.4V at -18mA. If you are using this buffer to drive another CMOS
input = with a gate capaci tance of 10pF, for example, how does the current
= -18mA relate to the 2.4V VOH min?
I mean if you are putting through 10Hz through the buffer and change = from
0 to 1, the input gate capacitance would be fully charged and won't = be
drawing any current.=A0 It surely won't be sitting at 2.4V.
So if we put together the situation of a CMOS buffer driving a 10pF =
capacitor at 70MHz over a very short line.=A0 The driver will be looking =
straight in to the capacitor.=A0 If the capacitor is big (100pF) then = the
VOH value will be affected since for a particular value of IOH it = will
take a certain time to charge up the cap.=A0 If the frequency of = operation
is high then it will be discharging before it has fully = charged.=A0 I can
see this.=20 However from the datasheet this relationship is not obvious if
my = thinking is correct.
If I know my load capacitance and have an IBIS model, can I ignore this =
VOH in the datasheet and verify that that the VOH of the chip works by =
using the slow setting of the IBIS model and simulating?
Thanks in advance
Chris
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