Pretty sure that the SOT 3 device will be a reverse voltage protection
diode for the opto LED diode. pf caps are not usually termed big ones.
I would ecpect that the charge pump circuitry is on the other side of the
opto.
Cheers,
Peter.
---------------------------
Peter Homann
http://www.homanndesigns.com/store
On Mon 16/04/12 1:43 PM , Jon Elson wrote:gene heskett wrote:
> Looking at the scope traces, either the probe is way out of calibration
> against the scopes own test square wave, or the 540 has a low value
series
> resistor, 33-120 ohm range, with several hundred pf on the other side
of
> the resistor as a noise filter on that input, and likely on all inputs
> since engineers have a tendency to 'step & repeat' for that stuff.
>
It was described earlier that the charge pump input to the G540 is
capacitively
coupled, and apparently has a large coupling cap. If it is driving the
base of a
BJT with the cap, that would require a pretty big one.
Jon
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