Evaluation of Multiphase Buck Converter for FPGA Power Delivery Networks

Sammanfattning

Evaluation and modeling of the Voltage Regulator Module (VRM) in FPGA Power Delivery Networks (PDNs) is a challenging task. With large and rapidly changing load currents in the FPGA, the PDN must ensure that the supply voltage of the FPGA is within its tolerance range. To meet this requirement, a multiphase buck converter used as the VRM in FPGA PDNs is investigated. The output voltage ripple and efficiency are evaluated for different numbers of phases and load currents to mark tradeoffs between them. Furthermore, three lumped equivalent circuit models are investigated and fitted to the measured output impedance of the converter to study their applicability for impedance modeling in PDN design. Finally, non-invasive methods such as load steps and impedance measurements are compared to invasive voltage injection, or Bode measurements, in terms of stability evaluation. The results show that increasing the number of phases improves ripple performance, but reduces efficiency at low loads. Lumped models can represent general impedance behavior, but different models introduce tradeoffs between conservative PDN design and overall curve fitting. Finally, load step testing offers a useful approximation of stability metrics, while the impedance-based stability method is limited to qualitative stability assessment for this converter topology.