Silicon oscillators?

Dave Paton

Has anyone used one with an SX? Linear has a part that interests me greatly (PDF link: the LTC6905) that is cheap, rugged, and really really tiny (SOT23-5). Oh yeah, and I have a few in a little box on my desk....

I'm just loking for thoughts. They're obviously designed for 3.3V operation, but will run at 5V pretty happily. They're nto as accurate as crystals, but are infinitely better than an RC, and around the same price point at resonators with one very important point: They have an output enable pin. My thought is this: Use one of these little buggers to drive an SX, and use the /OE pin to kick off the oscillator when an SX_Key is plugged in, thus preventing any smoke, fire, explosion, or general electronic unhappiness.

-dave

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This is not a sig. This is a duck. Quack.

Guenther Daubach

Dave,

I don't have experience with the LTC6905 but in one application I have used the ICS501 which is a PLL clock generator, also having an clock enable pin.

Like you, I thought it would be nice to disable the clock output as soon as an SX-Key would be connected. The problem is that while the SX is programmed, the programming voltage Vpp (about 12 Volts) is fed into the OSC1 pin. In case of the ICS501, it pulled down Vpp, so that the SX-Key reported an "Vpp Generation Failed" error, and the SX could not be programmed. Fortunately, the ICS501 did not get fried - maybe because the Vpp source in the SX-Key has a relatively high impedance.

I'm not sure if the LRC6905 can stand this voltage on its clock output pin, and if it possibly does not pull down Vpp.

As you have some in a little box on your desk, be brave, and give it a try - the SX community will be thankful hearing about your results .

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Greetings from Germany,

G

Paul Baker

One thing you need to worry about when using clock gen products which have an output enable is that quite a few of them continue to drive the line when output is disabled (a constant high or low, but not oscillating the line) this is unsuitable for plugging the SX-Key and programing the SX if the physical connection between the oscillator and the SX·is still there. My last project had a surface mount·oscillator on it with an output enable, but I also installed a SPDT switch to manually switch between the SX-Key and the oscillator (this informaton was provided to me by pjv, thanks Peter). Keep this in mind before you have a PCB fabbed.

One additional thing, using an active drive clock generator and plugging the SX-Key in with the clock gen still running will likely destroy your SX-Key

Post Edited (Paul Baker) : 4/15/2005 5:21:34 PM GMT