The experience of Thermal Design for PCBs Controlled by FPGA

2018-12-05 11:57Writer: qyadminReading:

  Modern times has observed miniaturization, integrity and modularization of digital products, resulting in the increase in conditions of assembly density of digital components and reduction in conditions of effective thermal dissipation area. Therefore, thermal design of high-power digital components and thermal dissipation problems at table level become so common among digital engineers. For FPGA (field programmable gate array) system, thermal dissipation is one of the pivotal systems determining if the chip is with the capacity of normally working. The goal of PCB thermal design is to diminish the temperature of components and the panel through appropriate steps and methods to make system work under ideal temperature. Regardless of numerous actions to dissipate warmth of PCBs, some requirements must be studied into consideration such as thermal dissipation cost and practicability. This short article arises with thermal design options for PCBs managed by FPGA system predicated on the evaluation of the useful thermal dissipation problems to guarantee the excellent thermal dissipation capacity for FPGA system control plank.
 

 FPGA System Control Table and Thermal Dissipation Problem


  The FPGA system control table used in this short article mainly includes control chip FPGA (EP3C5Electronic144C7 with QFP bundle of Cyclone III series by Altera®), +3.3V and +1.2V power circuits, 50MHz clock circuit, reset circuit, JTAG so that as download interface circuit, SRAM memory space and I/O interface. The framework of FPGA system control panel is shown in Determine 1 below.

  

Thermal Design for PCBs Controlled by FPGA System

  Heat resources of PCB managed by FPGA system are based on:

  • Numerous types of power materials power for the control plank such as +5V, +3.3V and +1.2V and power modules will create massive amount heat when doing work for quite a while. Power modules won't normally work unless appropriate procedures are effectively used.

  • The clock frequency of FPGA on the control table is 50MHz with high density of PCB routing. The escalation of system integrity leads to high system power usage and necessary thermal dissipation steps should be produced to FPGA chip.

  • The PCB substrate produces heat alone. Copper conductor is probably the basic materials of PCBs and copper conductor circuit will create temperature with the exchange of current and power intake.

  Predicated on the evaluation in conditions of heat resources from circuit system managed by FPGA control panel, necessary actions to dissipate high temperature have to be taken up to FPGA control plank to be able to boost the balance and reliability of the complete system.


 Thermal Design of PCB Managed by FPGA Chip


  1. Thermal design of power

  FPGA system control table is linked to +5V exterior immediate current (DC) power that's needed is to supply a present greater than 1A. LDO chip LT1117 (with small SOT-23 SMD bundle) is found as the energy module that is with the capacity of transforming +5V DC power into +3.3V VCCIO interface voltage and +1.2V VCCINT VCORE.

  Based on the evaluation above, two LT1117 chips are needed along the way of power circuit design in order to meet up with the voltage requirements of +3.3V and +1.2V by FPGA. Steps to dissipate warmth of power modules along the way of PCB design are the following aspects:

  • To make sure fast thermal dissipation of power module supplying capacity to FPGA chip, temperature kitchen sink should be put into LDO chip when necessary.

  • Since power component generates high temperature after long-time working, certain distance must be managed between adjacent power modules. The length between two LDO chips LT1117 should be held 20mm or even more.

  • To conduce to thermal dissipation, copper plating should be completed independently on the area of LDO chip LT1117 as shown in Physique 2.

  

Thermal Design for PCBs Controlled by FPGA System

  2. Thermal design of through holes

  In the bottom of components with massive amount heat creation on PCBs or near them should be positioned some conductive metallic vias. Thermal dissipation vias are small openings penetrating PCB with a diameter in the number from 0.4mm to 1mm and with the length between vias in the number from 1mm to at least one 1.2mm. Vias penetrating PCB make the energy at the front end quickly exceeded to other thermal dissipation layers so that components on the hot part of PCB are instantly cooled off and thermal dissipation area is increased effectively and level of resistance is reduced. Finally, power density of PCB can be improved. The thermal design of through openings is shown in Number 3 below.

  

Thermal Design for PCBs Controlled by FPGA System

  3. Thermal design of FPGA chip

  Heat of FPGA chip mainly originates from powerful energy usage such as VCORE and I/O voltage energy intake, energy consumption made by storage, internal reasoning and system and energy usage made by FPGA while controlling other modules (video, radio modules for example). When design FPGA chip QFP bundle, a copper foil is put into the guts of FPGA chip with a size of 4.5mmx4.5mm and many thermal dissipation pads were created. Heat kitchen sink can be added when necessary. The thermal design of FPGA chip is shown in Shape 4 below.

  

Thermal Design for PCBs Controlled by FPGA System

  4. Thermal design of plating copper

  Plating copper on PCB can both raise the anti-interference capacity for circuits and promote thermal dissipation of PCBs. PCB design predicated on Altium Developer Summer time 09 usually features two types of plating copper: large area plating copper and grid formed plating copper. Large area remove designed plating copper includes a defect that long-time working of PCB can result in much heat era, which can make strip-shaped copper foil increase and fall off. Therefore, to be able to acquire excellent warmth dissipation capacity for PCB, copper plating should be applied with grid form and the bond between grid and floor network of circuit so the shield aftereffect of system and thermal dissipation performance will be improved. The thermal design of plating copper is shown in Body 5 below.

  

Thermal Design for PCBs Controlled by FPGA System

  Thermal design of circuit planks is playing a pivotal role in identifying working balance and reliability of PCBs and the dedication in conditions of thermal design methods is the most crucial consideration. This informative article discusses some procedures to dissipate temperature of PCB managed by FPGA system and ideal method should be found with the concern of cost and practicability.
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