Dan:
Yes, I have seen similar times. I once tried using them to pulse a 5MHz
(yes, MegaHertz) transducer with the '2803. Seemed to work. Never
pursued it doe to other factors.

As you may know, Sprauge (Allegro) spec's the turn-on time at 250ns typ
and 1us max. They "forgot" to give a test circuit. They don't spec a
rise or fall time at all.

One observation I have is that the smaller the load resistance, the
better the rise and fall times should be. This is because of lower gain
and therefor less Miller effect capacitance.

Another feature of these parts is that under low loading, they have low
saturation voltages. This means that they can be used as "protected"
buffers to "fragile" PIC input pins.


-- Rich


Dan Michaels wrote:
>
> I was testing the ULN2803 mentioned in another thread, and
> was amazed at how fast this chip is. I drove a 130 mA load
> 30 ohm resistor [5v - Vcesat(=1v)] at 2 mhz. Nice and clean.
>
> For those not familiar, the 2803 chip is an 8-channel darlington
> driver, rated at nominal 0.25usec turn-on/turn-off delays [ala
> 50-50 points] --> and it actually does this under load.
>
> Anyone else have experience using these chips at high-frequencies
> under load? I thought darlingtons were supposed to be slow.
>
> thanks,
> - dan michaels
> www.oricomtech.com
> ==========================
>
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