Spin Semiconductor

The sound sample (see link below) was taken from an SKRM module on power up. If I switch off and immediately back on again, there is NO noise but if I wait about 5 seconds and power up, the noise is there again.

The clip LED also flashes briefly when there is NO noise but remains on longer when there is a noise.

Any thoughts? I suspect the built-in output mute is not allowing the output coupling capacitors long enough to charge to VDD/2 as per the FV-1 datasheet, but why? Is the crystal taking too long to start oscillating?

Presumably when quickly turning power back on the caps have not fully discharged?

Thanks,

Phil.

http://www.4shared.com/mp3/8d3VYGfz/eTa ... noise.html

Hmmm, I don't know why that is happening. I'll try to see if I can replicate it here. It could simply be a chip that went bad after test, it is called "infant mortality" when a chip (or other electronic item) fails shortly after passing test.

Hi Frank, thanks for replying. I get the same behaviour from both my SKRM modules

Phil.

Hi guys! I also observed this phenomenon in all chips FV-1. Helped by setting 15pF capacitor on the leg to ground and Crystal. This significantly reduces noise at startup chip. Alex

Hi Alex. The SKRM boards already have that but if something changed at the assembly house then the value of the capacitor may need to change.

We are working on this outside the forum since the SKRM boards are an OCT product and I shouldn't use the Spin forum for it.

frank wrote:Hi Alex. The SKRM boards already have that but if something changed at the assembly house then the value of the capacitor may need to change.

We are working on this outside the forum since the SKRM boards are an OCT product and I shouldn't use the Spin forum for it.

This is not just a problem on the OCT SKRM boards, I have built a few of my own designs lately and have this same problem.

It has only occurred on builds that I have used the cylinder type of watch crystal with a 15p cap. Other builds with a ceramic SMD oscillator did not have this problem.

I have since been using a 100p cap to ground on the cylinder type oscillator and this has stopped the start up squeal. I hope this is of some use.

The noise is created because the crystal enters a high harmonic on start-up. Normally a cap will stop this and all is fine but the actual value may need to be adjusted as the crystals vary from one manufacturer to another.

frank wrote:The noise is created because the crystal enters a high harmonic on start-up. Normally a cap will stop this and all is fine but the actual value may need to be adjusted as the crystals vary from one manufacturer to another.

I know this is an old post but, a 47p cap or thereabouts cures this problem, just in case anyone else still has this issue.

any idea what would be a good sub?