Automatic Compensation and PMBus Compliance Simplify a 0.95V, 40A Power Design for the Kintex UltraScale FPGA

Overview:
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 MAX15301AA02 InTune™ point-of-load (PoL) controller. The circuit was developed to power a VCCINT rail on a Xilinx® Kintex® UltraScale™ FPGA, but it is also suitable for similar applications such as VCC1V8, VADJ_1V8, and VCC1V2 rails of Xilinx Virtex® Ultrascale FPGAs. Included in this reference design are a schematic, applications information, test data, and a bill of materials.

Design Specifications and Setup:
•    Input voltage: 10.8V to 13.2V
•    Output voltage: 0.95V
•    Output current: 40A
•    Output-voltage ripple: 15mV
•    Switching frequency: 400kHz
•    Efficiency: 89% with VIN = 12V at 20A 

Figure 1. Schematic of the MAX15301 buck power supply at fSW = 400kHz.

Applications Information:
This PoL regulator was chosen for this design due to its accuracy, small size, and ease of use. It uses the MAX15301AA02 InTune automatically compensated controller which accepts 12V input and generates 0.95V output with 40A current capability by driving external MOSFETs.

The 400kHz switching frequency is set by resistor R156 (7.15kΩ). The output voltage is set by resistor R81 (12.7kΩ) between the set pin and analog ground. The output voltage can be changed by changing R81. Refer to the Output Voltage Selection section of the MAX15301AA02 data sheet. The output voltage, switching frequency, and current limit can also be monitored and programmed via a PMBus™ serial connection using our PowerTool™ software. This gives the user the ability to margin their designs during operation.

To minimize switching losses, the MAX15301AA02 integrates an advanced, high-efficiency MOSFET gate driver with adjustable nonoverlap timing and load-variable gate-drive voltage. An internal switch BabyBuck regulator generates the gate drive and the internal bias supplies for the controller with low power loss. BabyBuck improves efficiency and InTune automatic compensation ensures stability while optimizing load-transient performance. This regulator has better than 1% load regulation at full load and excellent transient response.

Hardware Files:
Schematic
Bill of Materials (BOM)

InTune is a trademark of Maxim Integrated Products, Inc. Xilinx, Kintex, and Virtex are registered trademarks and UltraScale is a trademark of Xilinx, Inc. PMBus is a trademark of SMIF, Inc.

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