Calculation of Pull-up resistor

Thread Starter

Muhammad Salleh

Joined Oct 5, 2018
34
Hi Guys.

I have a query about the calculation of the pull-up resistor as well as bus capacitance. I was given a PCA9557 chip to assess. I am unsure of how to calculate teh bus capacitance. From the datasheet, it states that
upload_2018-10-31_11-35-10.png
so for the SDA line, the bus capacitance will be 8 + 8(9.5) since i am utilising all 8 io ports.
Additionally, the datasheet states a maximum of 400pf for the bus capacitance. But, from the formula, i calculated that it was wrong.

upload_2018-10-31_11-36-51.png
The SDA line schematic as i have drawn out given to me is as such...

The PCA9557 is connected to 2 other components here and sadly i am unable to find their load capacitance for their datasheet.

Component 1) https://aerocontent.honeywell.com/a...-Munitions/HRF-AT4520_Product_Data_Sheets.pdf
Component 2) https://www.psemi.com/pdf/datasheets/pe42452ds.pdf
 
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