The most basic implementation consists of a sense resistor, a current sense amplifier, and a trans-conductance amplifier. Figure 3-1 depicts this implementation. These components add a significant cost to the design and an additional area on the PCB.

Figure 3-1 PSYS Monitor Functionality Done With Sense Resistor and Trans-Conductance Amplifier

Some implementations use the sense resistor used in hot swap designs to implement input power path protection. An additional current sense amplifier and a trans-conductance amplifier are needed in this implementation, as shown in Figure 3-2. These two discrete approaches are susceptible to system noise and tend to have lower accuracy and higher propagation delays.

Figure 3-2 PSYS Monitor Functionality Using the Sense Resistor Used in Hot Swap Designs

Some hot swap controllers, such as the TPS2477x, feature an analog current monitoring output, which is a voltage output proportional to the load current, as shown in Figure 3-3. A trans-conductance amplifier is required to convert this voltage output to a current source proportional to the load current, which is fed to the ISYS pin of the VR14 controller. However, the accuracy and large-signal bandwidth requirements for PSYS™ implementation cannot be achieved through this approach.

Figure 3-3 PSYS Monitor Functionality Done With Hot Swap Controller With V_IMON Output and Trans-Conductance Amplifier