I've been working on a sensor module consisting of an Arduino Nano, which im using to power the peripherals, and the following sensors on its I2C bus:
SHT35 breakout board (MOD-1030) (10k pullups)
TSL2591 breakout board (logic level shifters + voltage regulator with 10k pullups on both sides)
As7262 breakout board (logic level shifters + voltage regulator with 10k pullups on both sides)
K30 C02 sensor (no resistors)
I want to know wheter I should remove the integrated10k resistors on the SHT35, TSL2591 and AS7262, as in my knowledge the i2c data lines, and thus the resistors are connected in paralele combined resulsting equivalent pullup resistance for SDA and SCL of 3.3k ohm. I am thinking about replacing all these resistors with two single pull up resistors (4.7k or 3.3k) this would also provide a much needed pullup for the K30.
Would this be good or should I leave the resistors on the module and not add any? I want is functining pull up resistors for all of the sensors. I am not able to accurately know the bus capacitance and thus not able to calculate the maximum pull up resistance value with the formulas from the Texas Instruments application report (http://www.ti.com/lit/an/slva689/slva689.pdf), I do however think a resistor in the 2.8 - 4.7K range should suffice.
I'm also wondering why both sides of the BSS138 logic level shifter of the TSL2591 and AS7262 are equipped with pull up resistors, why is this done? Does a pull up on one side of the shifter/regulator not pull up the voltage on the the other side?