FPGA Migration

This week I managed to replace the FPGA, FTG256 with TQG144. Replacing, or in other word migration between FPGAs with different densities is not very hard as long as they fall under the same family. In this case since they are both Spartan6 XC6S, the pin names and functionalities mostly stays the same. However, the I/O pins are now reduced. The newly replaced FPGA requires different decoupling capacitors for its operation. The value and quantity of the decoupling capacitors required, are provided by Xilinx (Spartan-6 FPGA PCB Design and Pin Planning Guide). Additional capacitors should be used to compensate for long tracks or unstable power supply.

The current design utilises 3 voltage regulators to achieve the 3 different voltage levels required. There are single chip solutions to produce all the required output voltages. The problem is that they are all switching regulators, and not linear. The differences between linear and switching regulators are shown in the table below:

Linear

switching

Low efficiency

High efficiency

High heat waste

Low heat waste

Low cost

High cost

Smaller in size and less complex

Larger in size and more complex

No ripple and low noise

High ripple and noise

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