The Fairchild FPF1320 dual-input single-output power switch is a unique IC that switches a load between two power sources. It behaves as a power multiplexer (or mux), using a digital select signal to determine which of the two 1.5 V to 5.5 V input power rails to connect to the output, and can handle a maximum of 1.5 A while blocking unwanted reverse current from flowing from output to input or between inputs. Each input channel is controlled by an internal MOSFET switch, avoiding the voltage drop that occurs when diodes are used to OR multiple power supplies together.
However, the FPF1320 is only available in a tiny 1 mm × 1.5 mm BGA (ball grid array) package, making it difficult for a student or hobbyist to use. To address that issue, this board mounts the chip onto a compact carrier with 0.1? pin spacing that makes it easy to use with standard solderless breadboards, and it also serves as a breakout for a USB Micro-B connector that can be used to supply one of the input power rails.
The board is configured so that the “B” power rail is preferred and will be selected by default when that power source is present. USB power is connected to this preferred rail, so the default behavior is for the board to select USB power when USB is connected and the alternate “A” power rail when it is not. This enables the common application of having a device that can be powered by USB or an external power supply, automatically choosing the appropriate source based on what is connected. The default behavior can be changed through a surface-mount jumper and overridden through the power select (SEL) input.
Since this board is a carrier for the FPF1320, we recommend careful reading of the FPF1320 datasheet
We carry a similar power multiplexer based on the TPS2113A that offers some additional features, including automatic switching with minimal voltage droop, a configurable switching threshold, and configurable current limiting.