I am likely making this too hard, but a bit of help sure would be appreciated! I picked up some FSAM75sm60A "NOS" ICs off ebay a while back for cheap....and I thought I might design a test bed for one of them....I was trying to "rough in" some component values from the data sheet, and things were going quite nicely until I got to the short-circuit-protection segment.....In the 2013 version of the PDF there is very little data on the selection of "Rsc, Rf, Rcsc and Csc"....In the 2014 version they suggest using 0 ohm current sense resistors and a value of 26ohms for Rsc on page 7 in "2nd Notes #5" .....later, on page 13 in "4th Notes #8" they go onto suggest: "In the short-circuit protection circuit, please select the RfCsc time constant in the range of 3 ~ 4uS." But no matter how many times I calculate the voltage drop across a Zero ohm current sense resistor, I simply can't make the drop across a 26 ohm resistor greater than Zero which, of course begs the question, "How do I calculate the time constant created by Rf, Csc and Rcsc when the drop across Rsc (26 ohms) calculates to 0V when placed in parallel with 0 ohm sense resistors?"
A link to the Data Sheet is here:
https://www.fairchildsemi.com/datasheets/FS/FSAM75SM60A.pdf
Obviously I am missing SOMETHING.....but if they have gone to the trouble of updating the PDF to suggest using 0 ohm sense resistors and a value of 26ohms for Rsc, why didn't they just go ahead and give the values for Rf, Csc and Rcsc and be done with it? I realize there is a wide range of values that **would work** if there were a voltage present (and obviously there must be some voltage on Pin10 when the current reaches 125A, but I am at a loss as how to figure out what it might be....).
I know it is a big ask, but if anyone has a few moments to look @ the PDF and can figure out what I am missing, I sure would appreciate it.
Thanks in Advance!
Fish
A link to the Data Sheet is here:
https://www.fairchildsemi.com/datasheets/FS/FSAM75SM60A.pdf
Obviously I am missing SOMETHING.....but if they have gone to the trouble of updating the PDF to suggest using 0 ohm sense resistors and a value of 26ohms for Rsc, why didn't they just go ahead and give the values for Rf, Csc and Rcsc and be done with it? I realize there is a wide range of values that **would work** if there were a voltage present (and obviously there must be some voltage on Pin10 when the current reaches 125A, but I am at a loss as how to figure out what it might be....).
I know it is a big ask, but if anyone has a few moments to look @ the PDF and can figure out what I am missing, I sure would appreciate it.
Thanks in Advance!
Fish