[SI-LIST] Re: How to select the pullup/pulldwon resistor
- From: "Bill Reams" <breams@xxxxxxxxxxxxxx>
- To: <mnudelman@xxxxxxxxxxx>, "peter zhu " <peter.zhu@xxxxxxxxxx>,<si-list@xxxxxxxxxxxxx>
- Date: Mon, 2 Dec 2002 07:59:07 -0600
{snip}
PS> Just recently I was working with a vendor who specified a pullup for =
the
open drain on their chips to be 3.01 K +- 1%. Of course when asked tehy
could not explain such a pickiness in values and eventually agreed to =
allow
4.7K 5% resistors :-)))))
{snip}
I've been on both sides of this "issue". In a past job I designed =
in-circuit simulators and emulators for a couple of microcontrollers. If =
I used a 3.32k pull-up on a line (the circuit would have worked fine =
with a value of 1-50k), guess what went into the reference designs and =
data sheets? So I'm certain that there are designs out there using 1% =
resistors without regard to why.
On the other side, with a pull-up similar to the above 1-50k value =
needed, I've seen reference designs published with pull-ups of 5k. One =
engineer I've worked with was much into copying reference designs =
without regard for what he was doing so. You can guess at the grief he =
got when trying to find 5.0K resistors for his circuit.
The moral of the story is to understand your parts and circuits instead =
of blindly copying someone else's work. Obviously Mr. Nudelman =
understands instead of just copying.
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