Quote from: razorfishsl on August 07, 2013, 11:53:25 PM

Quote from: Bluestreak66 on August 07, 2013, 04:59:05 AM

Quote from: razorfishsl on August 07, 2013, 02:51:27 AM

Possibly it might be better to use an SPI controlled VCO

There are some really 'cheap' solutions available. That way you can have a bit of software that increases the clock rate until the thing starts producing too many errors, then you just gradually 'slide' the VCO back down a few tens of KHZ

Take a look at silicon labs, they have a full range of products that can be picked up on ebay or group buys fairly cheaply.

What you will see is that the number of errors will increase as the frequency increases, so with a VCO you can 'trade off', also as the temp is a function of the speed you can slide the VCO Downwards if you start getting too hot, whilst still mining.

Only 'fly' i can see is If there is some sort of clock syncronicity between the USB circuit (UART/USB bridge) and the ASIC

My approach here is that I would like to get a stable voltage range for oscillators that are easily attainable from well known trusted sources (such as digikey, mouser, element14, ect) and post a list of these with resistor values. That way a oscillator and resistors can be purchase and install with some certainty that it will work. Having a dialed in frequency at which is not obtainable in a oscillator package is not very useful. Now if we had these in bare chip form and were making custom boards we would be having a different conversation. I am more interested in dialing in the voltage at a given frequency as I think that will be more useful. The only road blocks here are I see are heat dissipation (which I think are mostly in check at this point) and current delivery capability.

Far better to go for an internally regulated part, trying to get a very accurate external voltage is not easy and usually requires additional voltage regulation chips, plus there is no indication of the conditions a user is running under. Just because a test setup works with a particular clock setup is not really a solid indication that other setups will work the same, or indeed be non destructive.

As long as everyone realizes that you would have no feedback control, that is to say if the component values you choose trashes a certain number of ASICS, there in nothing you can do to control it, other than unplug the power from the device.(unless you have some sort of clock gating circuit)

I'm not particularly pro or con what you are trying to do (hell I've toasted more post 500$ chips than most), but it is important that you take into account variation of the devices.

As regards the inductor, if you say it is cool... then it is cool, but it is a little more complicated than just setting a reference.

Sorry I'm still not following you. I'm using the voltage regulator thats on the board here is the data sheet: http://www.aosmd.com/res/data_sheets/AOZ1021AI.pdf It samples the output voltage to keep it steady, it's closed loop operation, the output is contiouosly monitored . The resistor divider is used only to offset the voltage to the comparator and has no effect on the system other than the output voltage look at page 7 of the pdf. It's a synchronous buck design so the output stage consist of 2 switches, an inductor and smoothing cap, nothing else.