PCF8523 INT output pulled up to KL30 up to 32V

[ThorV]

I am planning to use the PCF8523 INT1 output to wake up a TJA1043 CAN transceiver in sleep mode. The PCF8523 INT1 open drain output will be connected to TJA1043 Wake pin with 100kohm pulled up to KL30 up to 32V operating voltage range. 

I know that the datasheet mentioned the output voltage has a max rating of 6.5V but since the INT1 is an open drain, a 100kohm pull up resistor should limit the INT1 current to 0.32mA (<<10mA INT1 max current rating). A 6.5V max rating seems very low for a VDS of a transistor.

I am hoping this is OK. Can someone confirm?

[ThorV · Accepted solution]

Hi Tomas,

I just thought that if the INT1 is being clamped at 13.7V if my KL30 is @32V, this is the same as having a voltage divider, which will increase my quiescent current. 

I will have to find another way to solve my issue.  You can close this thread.

Thanks again.

[TomasVaverka]

Hello Victor,

Your analysis is generally correct, using a 100k pull-up resistor would limit the current to a safe level (0.32mA), which is well below the maximum current rating for the INT1 pin.

However, we would still be violating the voltage max rating of that pin. Current is not the only limiting parameter. I assume that 32V seen on the drain/source of the MOSFET is sure to do harm. I have asked a designer for confirmation and will update this thread once I get his feedback.

Btw, would it possible in your application to use a resistor divider to keep the 32V potential at the Wake pin and reduce the potential seen at the INT pin?

BR, Tomas

[ThorV]

Hi Tomas,

Thanks for the reply. Unfortunately, we can't have a voltage divider since it will increase the quiescent current of our module during deep sleep mode.

I did some testing and when my KL30 is >14V, the INT1 output is being clamped to 13.7V so it looks like there is a zener protection on the INT1 pin to GND. If this will hurt the PCF8523 in the long run, then I would definitely avoid doing it.

Please update me once you hear back from the designer to confirm.

Thanks,