PCA9515A: internal pullup resistor value? Appropriate Part?

Hi Paul,

Paul Venginickal said:

First question:  What is the value of the internal pull up resistor to VCC on the 9515A/B parts?  Would a control line with a 10K pulldown resistor be enough to keep the device "disabled".

The first part of this question makes it seem like there are pull-up resistors present on SDA0/SDA1/SCL0/SCL1, this is not the case. There are no pull-up resistors internally on the I2C bus connections.

There is an internal pull-up resistor on the EN pin. The datasheet doesn't supply the exact value of this internal pull-up, but there is an input current spec. If we use the maximum value that the input current could be on EN (-20uA), then we can calculate based off VCC = 3.6V. 

VCC / input current = Rpu = 3.6V / 20uA = ~180kohm 

This is a rough estimate, I am probably missing something here, but 10kohm a strong enough pull-down resistance. 

Paul Venginickal said:

Second Question:  When disabled, the two sides are completely isolated correct?  ie. not traffic/current passes through the part?

This is correct. EN = GND would disable the drivers on the SDA/SCL lines. 

Paul Venginickal said:

Third Question: My application is a follows:  I have an always on low power consumption section (+3.3V) of the board with I2C peripherals.  Occasionally, I need to power on a high power consumption section of the board (+3.3V) w/ I2C peripherals to perform some functions and then power down.  Both sides are +3.3V.

Paul Venginickal said:

Is the PCA9515A/B the correct part to bridge the two sides?  Another more appropriate device?  The PCA9515 will always be powered, but disabled (question 1) most of the time.  

PCA9515 disabled via EN = GND (through 10k pull-down) would mean that the internal buffer drivers are turned off on the I2C lines when VCC is still powered. I see no problem with this in bridging the two sides. 

Regards,

Tyler