mfa298 wrote:The other possible pitfall of using resistors in a voltage divider is if there's some capacitance in the source or the pi that either needs to be charged or discharged for the value to change. By having large value resistors in there you'll be limiting the current that can flow which could introduce a delay between the module sending a signal and the pi registering it.
That's unlikely to be a problem in this case, but it can have an impact on certain types of peripherals.
Yes, need to take into account input capacitance. Also, no public documentation about this.
It can be assumed based on similar chips, that the capacitance is near 15pF. And also have some inductance.
So, input and output are RLC circuit.
10k resistor have low pass frequency cut near 1MHz and delay of 345ns.
Good enough to fast speed I2C bus.
Same problem apply to active shifter using FET
This is based on Philips application note, that recommend to use at fast speed (400kHz).
Frequency response of voltage divider can be improved adding a capacitive voltage divider, with internal 15pF capacitor on gnd side.
A screenshot of circuit simulation showing difference with capacitor.