A typical redundant power supply configuration is shown in Figure 9-7 below. Schottky ORing diodes have been popular for connecting parallel power supplies, such as parallel operation of wall adapter with a battery or a hold-up storage capacitor. The disadvantage of using ORing diodes is high voltage drop and associated power loss. The TPS259470x/4x with integrated, low-ohmic, back-to-back FETs provide a simple and efficient solution. Figure 9-7 below shows the Active ORing implementation using TPS249474x devices.

Figure 9-7 Two Devices, Active ORing Configuration

The linear ORing mechanism in TPS25947xx ensures that there's no reverse current flowing from one power source to the other during fast or slow ramp of either supply.

The following waveform illustrates the active ORing behavior when the supply rails are being ramped up sequentially.

Figure 9-8 Active ORing Response

Figure 9-9 Active ORing Response

When the bus voltages (IN1 and IN2) are matched, device in each path sees a forward voltage drop and is ON delivering the load current. During this period, current is shared between the rails in the ratio of differential voltage drop across each device.

In addition to supply ORing, the devices protect the system from overvoltage, excessive inrush current, overload and short-circuit faults at all times.