Thermal Design of FPGA Circuit Board

PCB heat dissipation design of FPGA core control board

In recent years, with the miniaturization, integration and modularization of electronic products, the installation density of electronic components has increased and the effective heat dissipation area has decreased. Therefore, the thermal design of high-power electronic components and the board-level heat dissipation of circuit boards have attracted the attention of electronic engineers. One of the key technologies of whether the FPGA control system can work normally is the heat dissipation of the system. The purpose of PCB thermal design is to take appropriate measures and methods to reduce the temperature of components and PCB board, so that the system can work normally at an appropriate temperature. Although there are many heat dissipation measures for PCB, it is necessary to consider the requirements of heat dissipation cost and practicability. In this paper, through the analysis of the actual heat dissipation problems of the FPGA core control board, the necessary heat dissipation design for the PCB of the FPGA control board is carried out, so that the FPGA control board has good heat dissipation performance when working.

1. FPGA control board and heat dissipation

Design an FPGA core control board for teaching and scientific research applications, which is mainly composed of main control chip FPGA, +3.3V and +1.2V power supply circuits, 50MHz clock circuit, reset circuit, JTAG and AS download interface circuit, SRAM memory and I/O Leading out the interface and other parts. The main control chip FPGA adopts EP3C5E144C7 in CycloneIII series QFP package of Altera Company. The structure of the FPGA core control board system is shown in Figure 1.

The main sources of heat on the FPGA core control board PCB are:

(1) The control board requires various power supplies such as +5V, +3.3V and +1.2V. The power module produces a lot of heat when it works for a long time. If effective cooling measures are not taken, the power module will become hot and cannot work normally.

(2) The FPGA clock frequency of the control board is 50MHz, and the PCB wiring density is high. With the increase of system integration, the system power consumption is relatively high, and necessary heat dissipation measures must be taken for the FPGA chip.

(3) The substrate of the PCB itself generates heat, and the copper conductor is one of the basic molding materials of the PCB. The resistance of the copper conductor-coated corrosion line itself is heated due to the loss of the alternating current power.

Based on the above analysis of the heat source of the circuit system of the FPGA core control board, it is necessary to take necessary heat dissipation measures for the FPGA core control board to improve the stability and reliability of the system.

2. PCB heat dissipation design of FPGA control board

2.1 Power cooling design

The FPGA core control board is connected to a +5v~b DC power supply, which is required to provide a current of lA or above. The power module chooses the LDO chip LT1ll7, which converts the +5V DC power supply into the +3.3VVCCIO port voltage and +1.2VVCCINT core voltage required by the main control chip EP3C5E144C7. The LT1117 is packaged in a small SOT23 chip.

Through the above analysis, it can be known that two LT1117 chips are needed to design the power circuit to meet the power supply requirements of +3.3V and +1.2V required by the FPGA. The heat dissipation of the power module is handled as follows during PCB design:

(1) Because the power module will generate a certain amount of heat when working for a long time, keep a certain distance when laying out adjacent power modules. Too close a distance is not conducive to heat dissipation. When laying out, set the distance between the two LDO chips LT11l7 to 20mm or more.

(2) Carry out separate copper coating treatment on the position where the LDO chip LT1117 is placed, which is conducive to heat dissipation of the power supply.

(3) If necessary, add a heat sink to the LDO chip to ensure rapid heat dissipation of the power module and provide normal power supply for the FPGA chip.

2.2 Heat dissipation via design

Place some heat-conducting metallized vias at the bottom of and near components that generate a lot of heat on the PCB. The heat dissipation via is a small hole that penetrates the PCB, and the diameter is about 0.4mm to 1mm. . . The aperture should not be too large, and the distance between the vias should be set at 1 mm to 1.2 mm. The via holes penetrate the printed circuit board, so that the heat on the front of the printed board is quickly transmitted to other heat dissipation layers along the back of the PCB, and the components on the heating surface are cooled quickly, and can effectively increase the heat dissipation area and reduce thermal resistance, increasing the power of the circuit board density.

2.3 FPGA chip heat dissipation design

The main source of FPGA chip heat is dynamic power consumption, such as core voltage power consumption and I/O voltage power consumption, power consumption generated by memory, internal logic, and the system, and FPGA control of its functional modules (such as video, audio modules, etc.) will generate power Therefore, it is necessary to dissipate heat on the FPGA chip as heat is generated. When designing the QFP package of the FPGA chip, a copper foil with a size of 4.5mmX4.5mm is added to the center of the FPGA chip, and a certain number of heat dissipation pads are designed, and heat sinks can also be added according to actual needs.

2.4 Copper clad heat dissipation design

PCB copper coating can not only improve the anti-interference ability of the circuit, but also effectively promote the heat dissipation of the PCB board. There are generally two methods of copper cladding in PCB design using AltiumDesignerSummer09 software, that is, large-area copper cladding and grid-shaped copper cladding. The disadvantage of large-area strip copper foil is that the PCB board will generate a lot of heat when it works for a long time, which makes the strip copper foil easy to expand and fall off. Therefore, considering the good heat dissipation performance of PCB, a grid-shaped copper foil is used in the design of PCB copper cladding, and the grid is connected to the grounding network of the circuit to improve the shielding effect and heat dissipation performance of the system.

Summarize

PCB heat dissipation design is a key link to ensure the stability and reliability of PCB boards, and the choice of heat dissipation method is the primary factor to be considered. The design and application of specific heat dissipation measures is the core issue of PCB heat dissipation. In this paper, when designing the PCB of the FPGA core control board, the analysis of the heat source of the FPGA control system is the starting point, and according to the actual heat dissipation requirements, the power module of the FPGA control board, the FPGA control chip, the heat dissipation vias and the copper heat dissipation are designed. The heat dissipation method adopted by the FPGA control board has the characteristics of practicability, low cost and easy realization.

The above is the PCB heat dissipation design technology of the FPGA core control board introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.