Time (4 ms/DIV)

Time (10 ms/DIV)

9.3 OR-ing Application Configuration

Basic redundant power architecture comprises of two or more voltage or power supply sources driving a single

load. In its simplest form, the OR-ing solution for redundant power supplies consists of Schottky OR-ing diodes

that protect the system against an input power supply fault condition. A diode OR-ing device provides effective

and low cost solution with few components. However, the diodes forward voltage drops affects the efficiency of

the system permanently, since each diode in an OR-ing application spends most of its time in forward conduction

mode. These power losses increase the requirements for thermal management and allocated board space.

The LM74700-EP ICs combined with external N-Channel MOSFETs can be used in OR-ing Solution as shown in

Figure 9-18. The forward diode drop is reduced as the external N-Channel MOSFET is turned ON during normal

operation. LM74700-EP quickly detects the reverse current, pulls down the MOSFET gate fast, leaving the body

diode of the MOSFET to block the reverse current flow. An effective OR-ing solution needs to be extremely fast

to limit the reverse current amount and duration. The LM74700-EP devices in OR-ing configuration constantly

sense the voltage difference between Anode and Cathode pins, which are the voltage levels at the power

is monitored by the Anode and Cathode pins of the LM74700-EP. A fast comparator shuts down the Gate

exceeds 50 mV.

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