The first example demonstrates automatic switchover from main power (IN1) to standby power (IN2). This architecture is commonly found on applications that require a secondary/auxiliary input to conserve power while keeping downstream loads on. When switching between main and auxiliary power, the voltage drop on the output should also be minimal to prevent the downstream load from resetting or entering a lockout condition.

In this first example, the system is prioritizing the 12-V main supply on IN1. When the 12-V supply drops below 7.6 V, the device will automatically switch to the 5-V auxiliary supply on IN2. When the 12-V supply returns, it will become the output supply again. Furthermore, the voltage drop on the output should be minimal, providing the output with uninterrupted redundant power.

To minimize the voltage dip on the output, the TPS2121 will be used in fast switchover mode. By configuring the device in external comparator control scheme (XCOMP), the voltages on PR1 and CP2 are compared to determine whether IN1 or IN2 is powering the output. However, unlike the XREF mode, described above in the manual switchover configuration, XCOMP does not connect an external GPIO signal to the CP2 pin. Instead, PR1 and CP2 are connected to IN1 and IN2 respectively, allowing a direct voltage comparison between the two input channels. PR1 and CP2 are connected to IN1 and IN2 with a resistor divider. If the voltage on CP2 is higher than the voltage on PR1, then IN2 will power the output. If the voltage on PR1 is higher than the voltage on CP2, then IN1 will power the output.