SNOU177 December   2020 LM74700-Q1

 

  1.   Trademarks
  2. 1Introduction
  3. 2Setup
    1. 2.1 I/O Connector Description
    2. 2.2 Board Setup
    3. 2.3 Schematic
  4. 3Operation
    1. 3.1 Reverse Polarity Protection
    2. 3.2 ORing Application
  5. 4EVM Board Assembly Drawings and Layout Guidelines
    1. 4.1 PCB Drawings
    2. 4.2 Bill of Materials

3.2 ORing Application

When using the LM74700-Q1 as an ORing device, if the input supplies operate at slightly different voltages, the voltage at the common load point will follow the higher voltage. The LM74700-Q1 prevents reverse current flow from the common load point to the lower voltage supply rail. This test uses two LM74700DDFEVMs with 15 V at the input of the first EVM and 12 V at the input of the second EVM and the output of both the EVMs are shorted. As Figure 3-3 shows, the 15-V source at EVM1 is turned off for a period of time and the output (CH2) drops to 12-V source from EVM2. When the 15-V source is turned on again, the output rises to 15 V from EVM1. CH1 shows the input to EVM1, CH2 shows the output and CH3 shows input of EVM2.

GUID-875F6385-A769-4A65-BE18-E74EF6860967-low.png Figure 3-3 ORing Application – Higher Supply Switchover

Next, the 12-V source at EVM2 is turned off for a period of time and turned on again, the output (CH2) does not change. Figure 3-4 captures this test.

GUID-E746C323-03B6-4E03-8794-391684E0D88A-low.png Figure 3-4 ORing Application 12-V – Lower Supply Test