wiki:ventana/thermal_management

Version 2 (modified by Ryan Erbstoesser, 2 months ago) (diff)

combine faq and other thermal information into this one generic thermal management page.

Thermal Management

This page is made to help create an understanding of thermal management Gateworks Single Board Computers (Ventana, Newport and others).

Related links:

Heat is related to power. The more power the board draws, the more heat that must be dissipated.

The number one item that will be warm is the CPU. CPUs from Gateworks should all be equipped with a heatsink and depending on the CPU speed a fansink may be required.

Gateworks boards use components that are rated from -40 to +85C and higher (for example most CPU's and powersupply components have higher temp ratings). Note the +85C is the max rating for the component temperature which specifies the max temperature the component is guaranteed to work. The max ambient temperature for the overall product will be lower and is dependent on the effectiveness of the cooling solution used (enclosure, airflow, heatsinks, etc...).

The second item that will be warm will be any wireless radios that may be used. These typically consume a lot of power and thus will become warm.

Another item that is warm may be the PCIe switch (used on certain boards). The typical power usage is appx 1.35W up to a max of appx 2.6W (max being 85% traffic). The switch does support PCIExpress Active State Power Management (ASPM)and also will power down unused SerDes lanes automatically to reduce power when possible. Some customers choose to place a heatsink on the PLX PCIe switch chip.

To summarize:

  • Heat is a direct relationship with power consumption
  • Heatsink the CPU to a metal enclosure for better heat dissipation and/or use airflow
  • Add a heatsink to the PCIe switch chip if desired
  • Add a fan to dissipate the heat and avoid hotspots - use a fan to blow air over the board and radios to help cool them. This can be very effective even in a sealed outdoor enclosure.
  • Gateworks Shop - Heatsinks

Thermal & Enclosures

A successful technique has been to heatsink the processor to an exterior metal enclosure which essentially makes the entire enclosure a heatsink with lots of surface area for dissipation. This can also be done with wireless radios.

  • Heatsink the CPU to a metal enclosure for better heat dissipation and/or use airflow
  • Add a fan to dissipate the heat and avoid hotspots - use a fan to blow air over the board and radios to help cool them. This can be very effective even in a sealed outdoor enclosure. Gateworks sells an outdoor enclosure in which there is a small fan which circulates the air inside to help even out any hot spots on the CPU and radios. This fan alone typically lowers the CPU temp by around 15C. Outdoor Enclosure
  • It is possible to couple the radios to the enclosure with thermal pads.
  • Thermal Pads: Thermal pad material can be used. The thermal pad is applied to the top of the radio or CPU and the board is mounted so this pad then makes contact with the side of the enclosure. The pads are available in a variety of thicknesses which allows you to optimize it for your enclosure mounting. Here is a link for an example of the type of thermal pad that customers often use:

An example of using a heat slug to mate the CPU with the metal enclosure can be seen in use with the Gateworks Indoor Enclosures:

Maximum Ambient Board Operating Temperature

Almost all Gateworks standard products are defined as industrial temp (see respective board datasheet) with an operating temperature of -40C to +85C with adequate airflow. This means that the components used on the board are all rated for that temperature range or better. Typically power consuming/heat-producing processors will have a max operating temperature that exceeds this specification.

For example the following components are used on Ventana boards:

  • IMX6Q - Automotive temperature grade -40C to +125C
  • IMX6DL - Industrial temperature grade -40C to +105C
  • DDR3 - Industrial temperature grade -40C to +95C

We are often asked for the max ambient temperature a board can be operated at. This depends on the following:

  • Max temperature of the components on the board (you can't exceed any part's max operating temperature)
  • Active airflow (which will help to reduce heat from components that are hotter than ambient)
  • Enclosures (need to be able to dissipate internal heat to their environment otherwise over time the internal temperature keeps rising)
  • Power consumption (which is a factor of what your application is doing on the board and what peripherals you have added)

In order to determine the maximum ambient temperature you can operate at, you need to ensure that the components themselves do not exceed their max operating temperature. The components that consume the most power and thus produce the most heat are the ones that you want to focus on. If your board uses an Automotive grade CPU with a max operating temperature of 125C you can work backwards by raising the ambient temperature the board is operating under (within any intended enclosure) until the CPU has reached its maximum temperature. The difference between the CPU's internal temperature sensor reading and the ambient temperature is the thermal resistance of the board with respect to ambient. You will find that this value varies per board (depending on the board size, thickness, layers, copper) and also varies greatly on the power consumption (which varies depending on your application).

This evaluation process needs to take place within the enclosure you intend to operate within. You will find that the smaller the enclosure the more difficult it will be to get heat out of the enclosure. This depends on the thermal resistance of the enclosure itself with respect to its ambient.

Once you determine the max ambient temperature the board/system can operate within under your system parameters (peripherals, and application), you can do the following to increase this maximum:

  • Increase airflow which helps cool the components that exceed the ambient temperature (such as the CPU, DRAM, power supply)
  • Decrease the board's thermal resistance by adding or increasing the mass and surface area of heat-sinks

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