I'm using 100 kHz I2C for communication with 12 slaves. I found that MAX capacitance is about 400 PF. when I calculate the pull up resistor value, it looks like i can go mucher higher in capacitance. Is this correct?
Using 5V, and VOL = 0.4V for IOL = 3mA
Rmin=5V−0.4V /3mA = 1533 ohm This means I can go as low as 1533 ohm.
If C bus is 650pf
Rmax=1000ns/(Cbus*0.8473) = 1000ns/(650PF *0.8473) = 1800 ohm.
So If I choose a pull up resistor about 1.8K, It will satisfy BOTH Rmin and Rmax equitation. My Bus can handle up to 650 PF capacitance.
Is this correct or do I miss something? Why goes official specs for 100kHz maximum till 400 pf?
Thanks!! All Equitations comes from official I2C specs http://www.ti.com/lit/an/slva689/slva689.pdf
(PS: The I2C devices I use can also handle up to 20mA IOL for VOL = 0.4V. This means that Rmin can be way lower; Rmin=5V−0.4V /20mA = 230 ohm. My bus can handle much more capacitance)