Current limit switches are integrated circuit devices that features a current limited switch on its load. They are utilized in applications where a heavy capacitive load or even short circuit loads may be encountered. Current limit switches provide short circuit and over current protection by actively sensing the current and detecting if it exceeds a current limit threshold. They may have one switch, or incorporate multiple switches to make them well suited to the application. Applications include protecting interfaces that combine data and power on the same connections, such as USB.

 

The devices work by providing an upper limit to the current that can be drawn from them. This is called a constant current mode and occurs when the current drawn by the load exceeds the threshold set by the device. Devices are to operate with a certain over-current response time, which is usually required to be as fast as possible to minimize the possibility of damage to the circuitry. They can have built in soft start capability to ramp a power supply. Rise and fall times are controlled to minimize current surges when devices are turned on or off. Many switches have inbuilt transient voltage suppressors (TVS) to eliminate high positive or negative voltage spikes.

 

Current limit switches are usually rated for a continuous current flow through each channel they are providing a limiting function. They may have fixed current limits to correspond to an interface specification, allowing the product to comply with regulations and be sold. They may also have user adjustable threshold settings. Current limit switches will also typically implement other features associated with their application. This includes high electrostatic discharge protection; reverse current blocking and over temperature protection.