What Does Open Drain Mean ?

Open drain output circuits :

Open drain is a type of output circuitry commonly used in electronic devices, particularly in microcontrollers and digital signal processors. In an open drain output, the output transistor is connected between the output pin and ground, rather than between the output pin and a power supply voltage. This means that when the output is in the "high" state, the transistor is turned off and the output pin is effectively disconnected from the circuit. When the output is in the "low" state, the transistor is turned on and the output pin is connected to ground.

Open drain outputs are often used in digital communication protocols such as I2C and SMBus. In these protocols, multiple devices can share the same communication bus, and each device is responsible for driving the bus either "high" or "low". By using open drain outputs, the devices can easily pull the bus low, but do not need to be able to actively drive it high, as other devices on the bus will do that when necessary.

Open drain outputs can also be used to implement simple voltage level conversion between two circuits that have different voltage levels. In this case, the open drain output is connected to a pull-up resistor that is connected to the higher voltage level, and the output can either be driven low (connecting to the lower voltage level) or allowed to float high (connecting to the pull-up resistor and the higher voltage level).

Open drain is a term used in electronics to describe a type of output circuit that can only sink current, but not source it. An open drain output consists of a transistor that is connected between the output pin and ground. When the transistor is turned on, it allows current to flow from the output pin to ground, effectively sinking the current.

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