Low pass filter for uPC1237 on pin 2

[Greg Erskine]

Hi all,

I need a little help determining the correct values for the low pass filter for the DC detect input (2) for the uPC1237 speaker protector IC.

http://www.datasheetcatalog.org/data...ec/UPC1237.pdf

In the "Typical Application Circuit" on page 3 they use a 56k resistor and a polarised 300uF cap. After doing way to my research I have reason to doubt if these values are actually suitable. So am I missing something.

I have seen completely different RC values, giving better time constants, which seems important to me as it effects the speed of DC detection. Some use non-polarised caps (or back-to-back polarised caps) which seems sensible because the DC could be positive or negative. Others use second order filters instead of a first order filter.

I have read various texts, magazines, looked at many online circuits and even looked at the offerings on ebay. The differences in implementation has me wondering if I understand want is going on. Reading Rod Elliott's Loudspeaker Protection and Muting seems logical to me but contradicts most of the other solutions in one aspect or another.

regards

[Greg Erskine]

Bump