AW: Re: CEM 3340 chip problems

[Haible_Juergen#Tel2743]

>            Are these chips sensitive to stray capacitance or are they
>    defective. I have heard that these chips have not been  tested but I am 

>    surprised that so many seem to have problems. Has  anyone
>    else had problems with these chips?  Is the circuit layout I use for
>    testing  the chips critical?
>
> Sounds suspiciously like a power supply interaction.

There was a long article in Elektor about the CEM chips,
when they became available for DIY projects back then.
A few problems of the 3340 mentioned (from memory):

* They are not really intended for +/-15V supplies. -5V
   on the negative side give much better performance.
* The PWM comparator is prone to self oscillation, when
  there is too much stray capacitance. Use a positive
  feedback (RC-Network) to give it some hysteresis.
* The chips are very sensitive to interlock with other
  VCOs. Careful design of supply voltage decoupling
  is crucial for slow beat rates.

JH.

PS.: In my modular, one of the two 3340-type VCOs has
problems to start oscillating when power is switched on!
I can live with that (switching sync on and off cures the problem),
but it's still a strange phenomenon.