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Maxim > Design Support > Technical Documents > Application Notes > General Engineering Topics > APP 4033
Keywords: Fan Controllers, Fan Module, Fan Rack
APPLICATION NOTE 4033
Programmable Fan Controllers
Jun 21, 2007
Abstract:
As today's
systems achieve ever-increasing performance in smaller enclosures, their power
dissipation poses an increasingly serious problem. The need to maintain proper temperatures has
become critical in preventing thermal shutdown and even system failures. Thus, many systems now
require extra fans to maintain an adequate airflow. This application note provides an overview of fan-
control modules, and it presents a simple fan-controller circuit that uses the MAX6870 to monitor six
fans.
Overview of Fan-Control Modules
Large telecom and networking systems often employ high-performance processors that allow greater
functionality within a single "rack." For example, a line card that once supported 12 ADSL lines can now
support up to 64 lines. As a result, circuit boards that once dissipated 24W (2W per ADSL line) must now
dissipate 128W. That level of dissipation can be accommodated with a strongly forced flow of cool air
that reduces the pertinent thermal resistance.
Most telecom systems include a large number of fans. To ensure proper operation in the event of a fan
failure, the system usually includes more fans than needed (N+1 structure), so a typical system might
have six to eight fans. Each fan has its own power supply, so the fans are easily replaced without
powering down the system. A sub-rack fan assembly (Figure 1) includes multiple fan modules (six in this
case), supplied by a -48V battery bus and monitored by a fan-control module.
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