6 Extraction of Platform Current Information With Multiple PSYS Monitors Connected to the Same PSU

With the gradual increase in processor power consumption, the server power distribution boards (PDB) house multiple VR controllers and power stages to feed power into several CPUs. Each VR module is attached to the individual CPUs. In this architecture, only one VR14 controller attached to a CPU, suppose the CPU-1, is the recipient of PSYS data and associated connections to implement PSYS functionality as shown in Figure 6-1. All other VR14 controllers attached to the CPUs other than CPU-1 do not require PSYS functionality to be implemented. Only one VR14 per board requires PSYS considerations. This helps in moving from power monitoring at the individual CPU VR controller level to total platform power or current monitoring. The outputs of all the PSYS monitors need to be summed together to get the total platform input current.

Figure 6-1 Protecting Individual VR Controller Power Paths Separately by Incorporating Multiple eFuse Modules Connected to the Same PSU

Multiple eFuse modules (either a single TPS25984, TPS25985 or TPS25990 eFuse or a parallel combination of TPS25990 and TPS25984/5 eFuses for higher current designs) are required to protect the different power paths (feeding to each VR14 modules) separately in a multiple CPU board. However, all these loads are fed by the same PSU. Therefore, it is essential to monitor the PSU current when implementing the PSYS functionality. These eFuse modules serve the purpose of multiple PSYS monitors connected to the input power supply of the platform. In this architecture, the current monitoring outputs from all these PSYS monitors need to be aggregated to determine the global platform power. However as discussed in Section 4, the IMON pin of the TPS25984, TPS25985 or TPS25990 eFuses serves two purposes: 1) setting up the over-current and scalable fast-trip thresholds; 2) monitoring the current flowing through it. Hence, the IMON outputs of the multiple eFuse modules cannot be directly tied together to get the total platform current. Otherwise, that might interfere with the over-current and short-circuit thresholds of the individual eFuses modules. The solution is here to use a non-inverting summing amplifier to sum up all the IMON voltage outputs (V_IMON = I_IN x G_IMON x R_IMON) from the individual eFuse modules.