According to PMP11254, the Rcs is 0.082Ohm(Package1206, R30), and we found it 0.09Ohm(Package2010, R34) in PMP8812.
I could not find an accurate method to determine the Rcs resistor expect the introduce information about CS pin in SLVSB97C page12.
So how could we calculate a proper current sense resistor (Rcs) accurately? What's the difference between 0.082Ohm and 0.09Ohm, and how to choose the Package 1206 or 2010？
Hi Alex,
Please take a look at section 2.7.2 in this app note: http://www.ti.com/lit/an/slva305c/slva305c.pdf
The CS threshold value varies from IC to IC. I use the minimum CS threshold value to calculate the sense resistor value. For example: TPS23754 below I would use 0.5V.
There will be tolerances to take into account. The peak current will vary with input voltage, duty cycle and primary transformer inductance. The transformer magnetizing current and slope compensation will also add to the peak current.
You can attempt to calculate all of these tolerances or just select a standard sense resistor value about 15-20% lower than the value calculated using equation 21 from section 2.7.2 of the app note.
