Low Output-Voltage Ripple (7mV) Design for 1.0V, 5A Kintex Ultrascale FPGA Rail

Overview:
This reference design provides a power-supply circuit with an input voltage of 10.8V to 13.2V, an output voltage of 1.0V, and an output current of 5A using the MAX20751 and VT1697 chipset. The circuit was developed to power a MGTAVCC rail on a Xilinx® Kintex® Ultrascale™ FPGA, but it is also suitable for similar applications such as the MGTAVTT rail of Xilinx Virtex Ultrascale FPGAs. Included in this reference design are a schematic, applications information, and a bill of materials.

Design Specifications and Setup
•    Input Voltage: 10.8V to 13.2V
•    Output Voltage: 1.0V
•    Output Current: 5A
•    Output-Voltage Ripple: 7mV
•    Switching Frequency: 600kHz
•    Efficiency: 85% with VIN = 12V at 5A 

Figure 1. Schematic of the MAX20751 and VT1697 buck power supply at fSW = 600kHz.

Applications Information
This PoL regulator was chosen for this design due to its accuracy, low output-voltage ripple, and ease of use. It uses the MAX20751 and VT1697 chipset. The MAX20751 controller is configured for single phase, accepts a 12V input, and generates a 1.0V output with 5A current capability by driving the external VT1697 smart slave with integrated current and temperature sensors.

The 600kHz switching frequency is set by resistor R900 (80.6Ω) between the R_SEL3 pin and analog ground. The output voltage is set by resistor R935 (402Ω) between the R_SEL2 pin and analog ground. The output voltage can be changed by adjusting R935. Refer to the Program the Output Voltage section of the MAX20751 data sheet. The output voltage and current limit can also be monitored and programmed via a PMBus™ serial connection using Maxim Integrated’s PowerTool™ software. This gives the user the ability to margin their designs during operation.

An internal integrated switching regulator generates the gate drive and the internal bias supplies for the VT1697 smart slave with low power loss to improve the efficiency. This regulator has better than 1% load regulation at full load, excellent transient response, and less than 10mV of output voltage ripple.

Hardware Files
Schematic
Bill of Materials (BOM)

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

© 2015 Maxim Integrated