How to build a 0.95V, 40A power supply for an FPGA

February 12, 2015 // By Graham Prophet
Maxim Integrated has posted an application note detailing a reference design in which automatic compensation and PMBus compliance simplify a power design for the Kintex UltraScale FPGA (from Xilinx).

Maxim’s abstract for the note reads; “This reference design provides a power-supply circuit with a 10.8V to 13.2V input voltage, 0.95V output voltage, and 40A output current using the MAX15301 InTune point-of-load (PoL) controller. The circuit was developed to power a V CCINT rail on a Xilinx Kintex UltraScale FPGA, but it is also suitable for similar applications such as V CC1V8, V ADJ_1V8, and V CC1V2 rails of Xilinx Virtex Ultrascale FPGAs. Included in this reference design are a schematic, applications information, test data, and a bill of materials.”

Figure 1 The power supply/regulator schematic; a detailed version is here.

The design yields a regulator with the following specifications;

Input voltage: 10.8V to 13.2V

Output voltage: 0.95V

Output current: 40A

Output-voltage ripple: 15 mV

Switching frequency: 400 kHz

Efficiency: 89% with V IN = 12V at 20A

Figure 2 Transient response.

Accuracy achieved is measured as 0.9451V at no-load (0A) to 0.9407V at 28A (0.52 and 0.98% eroor, respectively, and transient response is measured at “soar” and “droop” on the ouptut in response to a 25 to 75% load step, of 29 and 31 mV, respectively.

Find the note at;