I am wondering how do we calculate the power supply current requirement for the following two devices.

1- PCF8574A Remote 8-Bit I/O Expander for I2C Bus
2- SC18IS606 I2C-bus to SPI bridge

The datasheet of PCF8574A says that the I/O current is around 25 mA. Is this the power supply current ? I don't think so. The I/O current need to be provided by the FPGA/MCU and is not the power supply current, is that right ? The datasheet also says in table 6.1 that the continuous current through VCC or GND is +/-100 mA. Kindly let me know which number should I use for power supply current.

The datasheet of SC18IS606 says that high and low I/O currents is 20 mA and 8 mA respectively.
The datasheet also says that the operating supply current is 4 mA. Which one should I use as power supply current ?

The links to the datasheets:
https://www.ti.com/lit/ds/symlink/p...c%2Fgeneral-purpose-ios-gpios%2Fproducts.html

https://www.nxp.com/docs/en/data-sheet/SC18IS606.pdf

 

The current that those components use will depend on how they are being used, and what the rest of the circuitry is. The operating current in the data sheet is just the current the internal circuit of the device requires. The rest will be current used by the I/O and supporting components.
If you really want to know how much current your designed circuit will require, breadboard it and make some measurements.

 

For PCF8574A, 8-Bit I/O Expander for I2C Bus, the I/O current in the datasheet is described as 25 mA. We know that it is not possible that all the I/O will be operating at the same time because the PCF8574A is serial. There will be one I/O working at a time. This shows that 25 mA current is reasonable to include while calculating the power budget for PCF8574A at least.

 

"Absolute maximum" ratings are the absolute maximum current that you can send through a certain input or output without breaking anything.
Iol=25mA is the maximum current that the device will deliver to a load.
Icc is the operating current, (the current which flows into the Vcc terminal and out of the GND terminal, which is 10uA in standby and 100uA when operational.

So you have to allow for 100uA plus anything you have connected to it, and possibly the current through the SDA and SCL pullup resistors when the clock or data are driven low.

 

For SC18IS606, the operating supply current is 4 mA. According to datasheet the pull up currents for VDD 3.3 V is 50 uA to 90 uA.

Does it means that we can not use 10 kohm for pull up SDL and SDA ? the gives 0.33 mA as pull up current.

If I am not using the I/O in SC18IS606, then the I/O currents 20 mA and 8 mA respectively are not applicable.

I guess it is quite ok to use 4 mA or maybe 5 mA in power budget calculation for SC18IS606.

 

According to datasheet the pull up currents for VDD 3.3 V is 50 uA to 90 uA.

That refers to the built in pullups on the GPIO, not the SDA/SCL pullups.
Why do you need an I2C to SPI bridge? I don't know of a microcontroller that doesn't have both.

 

for the 8574 device I would provide power supply capability of100mA. for the 181S606 device it seems you only need to provide 5 mA of supply capability. This is based on y reading of the data sheets.