Mcp23008 problem

i2c

i am using mcp23008 that is a i/o expander ,everything is OK but in datasheet there is a capacitor and i don't know what is that doing ,also i didn't see it in any designed board that i found in internet .
do you know what is that and it is necessary to use or not
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Best Answer

This capacitor is only used in Microchip's testing setup for deriving "real world" rise / fall times of data edges - it models the input impedance of other devices connected to the I2C bus. You don't need to include it in your circuit, and in fact it would be a very bad thing if you did as it would increase the load capacitance on the line - which ideally you want to be low.