Datasheet

Open Drain GPIO

The DS2413 outputs are "Open Drain". What that means is that the output is the "Drain" of an N-

channel FET:

Internally, the "Source" of the FET is connected to Ground. But the Drain is left open. When

switched on, the FET provides a path for current to flow from the output pin to ground.

Since there is no internal connection to VCC, the open drain output does not put out a voltage

like an Arduino GPIO pin. You have to provide your own external pullup. While this may seem

inconvenient, the open drain configuration allows for a lot of flexibility. Since the output voltage

is not dependent on the operating voltage of the breakout, you can use a variety of power

sources. The FETs in the DS2413 are capable of switching voltages up to 28v and up to 20mA.

The diagram below from the DS2413 data sheet (http://adafru.it/deP) shows how input and

output connections should be made - with an external pullup to a local power source.