There are many different types of power supply products in the lineup, and it may be difficult to select the right one for the first time. Here, we would like to introduce the types of step-down DC/DC converters often used in FPGA circuit design. We will compare the features and ease of design of linear regulators and switching regulators.
Features of Step-down DC/DC Converters
There are two types of step-down DC/DC converters: linear regulators and switching regulators. The table below summarizes the features of each. Linear regulators can be used for small current values requiring low noise. For applications that require high current and a tight thermal design, switching regulators are used.
|
Type |
Linear regulator |
Switching regulator |
|
Advantages |
Simple
・Low noise ・Low number of external components |
High efficiency |
|
Disadvantages |
Low efficiency
・High heat generation ・Poor load response |
High noise |
|
Applications |
For analog circuits
・Low power ・Low cost applications |
For high power logic circuits
・Applications requiring low power consumption |
Linear regulators
The most common linear regulator consists of input and output capacitors and a voltage divider resistor that determines the output voltage, as shown in Figure 1. Since it has a very simple circuit configuration, it is relatively easy to design. Even those who have never designed a power circuit can do so by reading the data sheet and selecting constants.
Also, unlike switching regulators, there is no switching operation, so noise is low, making them ideal for circuits that do not like noise, such as analog and PLL circuits.
It should be noted that the larger the difference between input and output voltages and currents, the more heat is generated. In particular, when making a low voltage from a high voltage of 12V or higher, or when a current exceeding 1A is required, please select a switching regulator while considering the selection of a suitable one.
Figure 1: Linear regulator
DC/DC converter with built-in power element (monolithic)
DC/DC converters with built-in power elements have more peripheral components than linear regulators and require an external inductor. Therefore, layout design is difficult, and the degree of difficulty is moderate.
Since they are more efficient than linear regulators, the power that can be supplied to FPGAs is also higher, and depending on the device, it is possible to supply about 10A.
Note, however, that the IC generates more heat because of the built-in power element, so thermal design measures, such as heat dissipation measures, are required when a current of 5 to 10 A is required.
Figure 2: DC/DC converter with built-in power element
Controller Type DC/DC Converter
In controller-type DC/DC converters, all power elements are external. This makes it possible to handle large currents by using power elements with low on-resistance and low switching loss. They are used in power supply circuits from 10A to 100A or higher.
However, since the power element is external, more components are required and the layout design becomes very complicated. The disadvantage is that the base area occupied by the power supply circuit is very large.
If you have no experience in power circuit design, we recommend that you avoid designing a high-current power circuit using a controller type DC/DC converter and select a module type.
Figure 3: Controller-type DC/DC converter
Module Type DC/DC Converter
Some module-type DC/DC converters can be designed with only input/output capacitors and voltage-setting resistors, making them easy to use for those who have no experience in power circuit design because they can be designed in the same way as linear regulators.
A wide range of products are available, from products supporting currents of 1A or less to those supporting currents of 200A or more, making them the ideal solution for boards with FPGAs. For this reason, they are also used in many evaluation boards for Intel FPGAs.
For multilayer boards with FPGAs, module products are recommended because a larger area of power circuits leads to higher costs, and because multi-phase operation using modules is more effective for high current and high-speed response.
Figure 4: Module-type DC/DC converter
Conclusion
We have explained the types of step-down DC/DC converters used in boards with FPGAs. We hope that you will consider the characteristics of each power supply device when selecting a power supply product for your FPGA or CPLD. If you have any questions about selecting a power supply product, please contact us. Our engineers dedicated to power supply circuits will be happy to assist you in selecting the right power supply product for your FPGA.
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