[sdiy] Another SSM2164 question

[Tom Wiltshire]

Hi all,

The subject says it all really. The VCAs in the SSM22164 require a  
500R resistor and 560pF capacitor to ground on each VCA input, as  
well as a resistor to convert voltage to current (30K in the datasheet).

Now, what I'd like to know is what do the 500R/560pF do and how are  
their values calculated? All the datasheet says about it is that "a  
500R resistor in series with a 560pF capacitor must be added from  
each input to ground to ensure stability". Great.

Practically, it seems you can vary the values a bit without incident  
(I've used 560R/470pF and nothing bad has happened) but it's a bit  
hard to know when you're not sure what they're supposed to prevent.

The datasheet is at:
http://www.analog.com/static/imported-files/data_sheets/SSM2164.pdf

Thanks,
Tom