In enterprise server applications, the latest Intel® VR14 specification introduces the requirement for accurate system input power monitoring. This allows tracking of average system input power, estimating the execution time of high power bursts, and signaling to reduce power when system input power exceeds a critical threshold. System input power can be directly monitored using an input-power signal or indirectly using system input current and system-input voltage as alternatives.
This application note demonstrates accurate and high-speed system input current monitoring using TPS25984, TPS25985, or TPS25990 eFuses to implement PSYS™ and PSYS_CRIT#™ in a VR14 multi-phase controller. This document begins with the definitions of PSYS™ and PSYS_CRIT#™, along with their accuracy and bandwidth requirements. Next, the implementation of the PSYS monitor is discussed. Then, the ISYS register and gain selection guidelines in conjunction with TPS25984, TPS25985, or TPS25990 eFuses are depicted, along with a design example. After that, the functional verification of PSYS™ and PSYS_CRIT#™ in the TPS536C9T VR14 controller are presented. Finally, the aggregation of the voltage outputs from multiple PSYS monitors connected to the same input power supply is illustrated in detail.
PSYS™, PSYS_CRIT#™, VR_HOT#™, and PROCHOT#™ are trademarks of Intel.
Fusion Digital Power™ is a trademark of Texas Instruments.
Intel® is a registered trademark of Intel.
PMBus® is a registered trademark of SMIF, Inc.
All trademarks are the property of their respective owners.
A typical server platform contains one or more processor units (CPU) as well as other sub-systems and is powered by one or multiple power supplies (PSU). In a broader sense, the PSUs are categorized as common redundant power supply (CRPS) and non-CRPS PSUs. CRPS PSUs have crisply defined peak power capabilities, whereas non-CRPS PSUs have no standard of behavior beyond their 100% rated power. The most critical case of PSU configurations is one where a single PSU is operational and that cannot handle all the projected peak power envelope demanded by the platform. Therefore, the total power drawn by the platform must be continuously monitored, and there must be a protection mechanism to throttle the power demanded by the platform quickly once a pre-programmed threshold is exceeded.
The system input power monitor, PSYS is designed to provide information necessary for the processor to dynamically allocate power between different system components, such as the CPU, memory, and the rest of the platform, within a designated power budget. This helps in optimal use of total available platform power by facilitating the dynamic employment of surplus system power to assist the platform turbo. In the absence of accurate system current monitoring, the platform designer sets the peak power limit too low, potentially settling for a too conservative power envelope. This results in sub-optimal utilization of available platform power.
PSYS_CRIT#™ is a must-have requirement in the case of non-CRPS generic PSUs to handle peak power events. Otherwise, these peak power events can, depending on their dwell time, shut down or damage platform power sources. Implementing the PSYS_CRIT#™ functionality enables the use of PSUs with generic specifications without making it mandatory to procure CRPS PSUs.