T2080 Refernce Design RTC INT Pin

[hemanttiwari199]

In T2080 Refernce board schematic, why INT PIN OF DS1339U-33+ RTC is Pulled up by 1.8V?

As the IC operating Voltage is 3.3V it should be pulled up using 3.3V and then using level translator it should connect to 1.8V of T2080 pin.

Can you explain the logic behind this connection?

Regards

Hemant 

[ufedor]

Please refer to the DS1339U-33 Data Sheet where it is written:

"The SQW/INT pin is an open-drain output and requires an external pullup resistor."

[hemanttiwari199]

yes, it is require pull up resistor, but my concern is related to voltage.

DS1339U works on 3.3V and SQW/INT pin is connected to t2080 IRQ pin having pull up resistor having 1.8V.

how the connection are going to work because of the pullup voltage difference?

[ufedor]

To understand how open collector/drain works it is needed to read, for example:

Open collector - Wikipedia 

[hemanttiwari199]

Can you please explain me using some reference ?