In the second example, the system seamlessly switches between two 12-V supplies, providing uninterrupted power to a downstream load. Priority is given to IN1, the main 12-V power rail, and switches over to IN2, the backup 12-V power rail, whenever IN1 dips. When the main power rail returns, the device will switch back to the main supply. Redundant power is critical in systems that require uninterrupted sources of power. If the output voltage were to dip on these systems, this could cause the downstream load to reset to enter an undervoltage lockout condition. Therefore, the TPS2121 will be used in fast switchover mode to minimize the output voltage dip.

Similar to the automatic switchover example shown above, the TPS2121 can be configured in XCOMP mode. However, to minimize the voltage switchover error for a more seamless switchover, an external precision regulator can be connected to CP2 in XREF mode. In this configuration, a REF3325 provides an external reference voltage on 2.5 V ± 0.15% (2.50375V). If the voltage on PR1 is higher than this external reference, priority will be given to IN1. If the voltage on PR1 drops below 2.50375V, then the device will switchover to IN2.

The design specifications detail the input voltage range for 12.1 ± 3%. Therefore, the resistor divider on PR1 is configured such that the voltage on the pin dips below 2.50375V before IN1 crosses 11.73 V (12.1 V – 3%). Once this occurs, the design will start fast switchover to IN2 within 5 us.

For additional information regarding this configuration, including full design procedures, schematics, and layout, please refer to TIDA-01638: Seamless Switchover for Backup Power Reference Design.