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[FAQ]: Priority Power MUX solution for high current high power application?

Part Number: LM7480-Q1
Other Parts Discussed in Thread: LM7481-Q1,

What is the recommended solution for high current Priority Power MUX application?

RELATED PRODUCTS: LM7480-Q1 and LM7481-Q1

  • Background:
    TI has integrated power MUX devices for <6A current requirements. Refer to the Application Note on the Basics of Power MUX. However, >6A applications, priority power MUX using LM7480-Q1 or LM74810-Q1 with external MOSFETs is recommended.
    Figure 1 shows the priority power MUX using LM74800-Q1 for high current applications.

    Figure 1: Priority Power MUX using LM74800-Q1

    Priority Power MUX Solution:
    When both the primary are present, then the priority should be given to the primary source and the system should be powered from the primary source path independent of the supply voltage levels. In the absence of the primary supply or when the primary supply drops to a specified under voltage level, then the downstream should switch over to the auxiliary power path.
    The OV connection of the AUX channel is from the primary supply path. The OV falling threshold of U2 is set at the under voltage level of primary supply. During normal operation, primary path is ON. OV of U2 is high and this keeps GATE of Q4 OFF, disconnecting the auxiliary supply path to the load. When the primary supply is dropped or when it reaches a set under voltage level, then Q2 turns OFF, disconnecting the primary path. At the same time, OV threshold of U2 goes low and HGATE starts rising after a delay of 6-μs (typical). HGATE has gate drive strength of 53 μA. Q5 enables higher GATE drive levels up to 600-μA for fast turn ON of Q4 . U1 on the primary path remains active keeping Q2 ON, as its Vs supply is powered from the auxiliary path. When the primary supply is connected back, then the system output immediately gets connected to the primary path. OV of U2 goes high and Q4 turns OFF in 3 μs (typical).

    Figure 2: Priority Power Mux – Switch Over from 12V Primary to 10V AUX

    Figure 2 shows the switch over from 12V primary supply to 10V AUX. When primary falls below 10V, OVP condition for AUX is cleared, OVP voltage falls below 1.1V and HGATE of AUX turns ON. VOUT transitions from 12V to 10V smoothly without any voltage droop during switchover.

    REFERENCE: DESIGN# 6 IN APPLICATION NOTE: SIX SYSTEM ARCHITECTURES WITH ROBUST REVERSE BATTERY PROTECTION USING AN IDEAL DIODE CONTROLLER