Choosing the value resistance of shunt.

Hello

I've discovered something that looks like a great chip: the FCM8201. http://www.fairchildsemi.com/ds/FC/FCM8201.pdf

My problem is that I don't know how to design (value of R) the Shunt resistors used to measure the global current.

Page 13 of the doc there are some explanations, which are a little bit... foggy for me. I think it's a usual design, which explain why there are a few explanations.

I don't find the way to link Rs to Is(max) (my choice) and I_in(max) (=1.4V).

I hope you'll be able to help me

Have a nice day

Try
http://www.fairchildsemi.com/an/AN/AN-8201.pdf

I found a solution to my problem, but now I face another one.

There are 3 levels of protection depending on V(I_In)

If V(I_In)>2.5V after 3 pulses the short circuit current protection is enabled. FCM8201 closes all motor drives and latches the close status. In order to go back to restore output the FREE pin have to go HIGH and LOW (start)

If V(I_In)>1.5V the cycle by cycle current protection is enabled. FCM8201 reduce the duty to minimum duty output.

If V(I_In)>1.4V the overload current protection is enabled. The time setting can be determined by a capacitor on the OC_TMR pin.

I_in = Rbias x Ibias + U_shunt
Ibias = 50µA Rbias= 10k
Then the cycle by cylce triggers when U_shunt=1V

(that is the answer of my first post)

Now:
Ushunt triggers at 1V
U= R_shunt_total x I_shunt
R_shunt_total = R_shunt / nb_of_shunt
I want that each shunt adds 10A
then R_shunt= U/R= 0.1ohms

Pshunt= U²/R= 10W
That toooooo much

In fact my problem is the Ushunt triggers at a quite high voltage.
I wonder if I can put a amplifier after the U_Shunt in order to multiply it by 5 or 10.
So I could have a Ushunt trigger at 0.5 to 0.1 which is much easier to design.

Lookinf forward to your help

Have a nice day