Low Profile Raises Thermal Efficiency

Jan. 1, 2005
Converters will help board-level system designers improve thermal efficiency and packaging density.

Astec Power has introduced a new family of 10-30W DC-DC converters in ultra-low profile, open-frame, surface-mount packages. The product line also offers board-level system designers improvements in thermal efficiency and packaging density.

The modules range in height from 7.7mm down to 4.2mm, giving designers a compact power solution with the low profile and PCB mounting flexibility needed to achieve the most space-efficient and lowest profile board layout. The thermal performance of board-level system design can also be improved by using these modules.

Astec Power's European technical support manager, Richard Kidgell explains, "In a system with forced air cooling, the low profile dramatically reduces the air pressure drop across the converter, minimising the thermal shadowing effect on devices mounted 'downwind'. The benefit is particularly noticeable when compared with modules using an industry-standard height profile of 0.5in. The benefits increase when combined with the packaging flexibility allowed by this low-profile surface-mount design."

CREATING SPACE In many board-level designs requiring compact packaging, mezzanine cards are used. They are mounted parallel to the motherboard, reducing the height above the board for components. If we take a 1U height profile ('pizza-box') as a common requirement, the gap remaining between the two boards will be around 30mm, once board thicknesses and enclosure clearances are accounted for.

Kidgell adds, "Since we have components on both inner facing sides of the slot, maximum component height has to be less than 15mm (30mm/2) to allow clearance. The thermal shadowing effect would almost certainly preclude the use of a converter with a conventional 0.5in height profile in such a location on the board, unless the power devices positioned in this narrow slot were heavily de-rated."

In contrast, the Astec devices pose little or no problem mounted in such a position. Rather they allow greater flexibility in component placement and layout on the mezzanine and motherboard, as there are no 'dead' areas above the low-profile modules. Thermal performance is improved because the full area of the board, including the section under the mezzanine, dissipates heat through the airflow.

Similar problems can occur in a standard racking system using multiple boards, where the card pitch is typically 25mm or 20mm. Here, Astec modules offer another advantage because they are designed for mounting on either side of a board, giving the designer greater layout flexibility, as well as providing a greater surface area by exposing both sides of the slot to the cooling air flow.

Kidgell says, "If multiple converters are needed, designers can place the surface-mounting Astec devices on power planes on both sides of the board. Again, this helps board layout and circuit density, as well as promoting heat dissipation from both sides of the board. Thermal performance is better because the additional power plane provides conductive and radiative cooling from the opposite side of the board."

FAMILY MEMBERS There are five different models in the range, each with single outputs choices from 1.0VDC to 5.0VDC. Multiple power ratings are available: 10W (AUM and AUD Series); 15W (AUG Series); 20W (AUG Series); and 30W (AUK Series). All have a nominal input voltage of 48VDC, plus a non-isolated 19.8W module (AVC Series) with input voltages of 3.3VDC or 5VDC.

The devices are suited to comms applications such as optical, wireless and broadband, where component heights are a concern. To improve space savings more, the modules meet CISPR22, Class A conducted and Radiated EMI standards, so they do not have external filter circuitry.

High efficiency (88-93%) and good thermal design support operating temperatures from −40°C to +85°C, depending upon the model and the cooling method employed.

All of the devices also offer alarm output (power good signal is not available on AVC Series), remote on/off, parallel operation (not available on AVC Series) and output voltage adjust (only available on AVC Series). In addition, there is protection from over-voltage, over-current and low voltage. All models except the AVC Series provide isolation up to 1500VDC.

These products meet worldwide safety and performance standards, including listings from UL and CE.

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