From the basic circuit of load switch, its characteristics are simple structure, but the drawback is the lack of overheat protection (if there is a local short circuit or output short circuit in the load). When a short circuit occurs, not only the load and the load switch are damaged, but also the entire device or system cannot work properly due to power overload cut-off. Therefore, in recent years, many improvements have been made according to the application status of load switches to improve performance, increase work reliability and add functions.
Add overheat shutdown circuit in the load break switch. If there is a local short circuit or short-circuit situation in the load, the core temperature of the load switch exceeds the overheat threshold temperature, and the overheat shutdown circuit will work and cut off the load switch. This not only prevents greater damage to the load, but also prevents the power from affecting other circuits due to load short circuits. When an overheat fault occurs, the load switch also outputs a fault signal to indicate the existence of a fault. In addition, it also has input undervoltage latch protection function.
Add a current limiting circuit to the load switch. There is no current detection and current limiting output circuit in the load switch. It has two structures: the limiting current value is set by the factory; the limiting current can be set by an external resistor. When an overcurrent state occurs, the load switch outputs a fault signal.
The load break switch with current limiting output not only improves work reliability and safety, but also can be used as a power distribution switch, hot-swappable socket, and USB port. Some load switches output latching (no output) when overcurrent occurs, then this load switch can be regarded as an "electronic fuse" and can work normally after eliminating overcurrent faults. Some load switches continue to supply power to the load at a limited current (constant current) when overcurrent occurs.
With the advancement of semiconductor technology, the on-resistance of individual discrete devices is decreasing year by year, and the on-resistance of devices with small on-resistance can be less than several mΩ. The on-resistance of the integrated load switch is slightly larger, and can currently be done to be about several tens of mΩ. In order to improve the performance of the switch including slow start (slow start means that when the switch is turned on, the voltage rise rate is a slope to prevent excessive surge current) and quick shutdown. There are several slopes of voltage rise: several slopes are set by the factory (with different start-up times) for users to choose; and users can set the start-up time by an external capacitor. A discharge circuit is provided in the load switch when the switch needs to be quickly shut down.
The load break switch is a universal power switching device. In the past, it was mainly used in industrial control and automobile industry. In recent years, with the development of portable electronic products, in order to save energy, in addition to using efficient power management IC, multiple load switches are also needed, and they are controlled by microprocessors to form load management (when different operating states, the useful load is powered, and the unused load is turned off). After the load switch is added with current limiting function, it can be used as a power supply port for computer peripherals, and can also be made into a hot-swappable power socket, or a power distribution switch.
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