Applications having two energy sources such as Portable battery powered equipment require preference of one source to another. For example, mains power (wall-adapter) has the priority over the internal back-up power or auxiliary power. These applications demand for switch over from mains power to backup power only when main input voltage falls below a user defined threshold. The TPS2663x devices provide a simple solution for priority power multiplexing needs.

Figure 10-12 shows a typical priority power multiplexing implementation using devices. When the MAIN power is present, the device in VIN_MAIN path powers the OUT bus irrespective of whether auxiliary power VIN_AUX is greater than or less than VIN_MAIN. Once the voltage on the VIN_MAIN rail falls below the user-defined threshold, the device VIN_MAIN issues a signal to switch over to auxiliary power VIN_AUX. The transition happens seamlessly in t_{OVP(dly_fast}), with minimal voltage droop on the output. The voltage droop during transition is a function of load current and output capacitance. See Equation 13.

Equation 13.

where

• V_(DROOP) is in volts, I_(LOAD) is load current in Ampere, C_(OUT) is output capacitance in µF, t_{OVP(fast_dly)} = 140 µs (typical)

Figure 9-13, Figure 9-14, Figure 9-15 and figure 9-16 show typical switch-over waveforms of Priority Muxing implementation using the TPS26630 or TPS26631 for 20-V Primary and 24-V Auxiliary Bus.

Figure 10-12 Priority Power Mux Implementation

Figure 10-13 VIN_MAIN Power Recovery: Change Over from Auxiliary VIN_AUX to Primary Power VIN_MAIN

A.

Figure 10-15 VIN_AUX Brownout Condition

Figure 10-14 VIN_MAIN Brownout Condition: Change Over from Main VIN_MAIN to Auxiliary Power VIN_AUX

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Figure 10-16 VIN_AUX Power Recovery