Fan Speed Controller

Linear Technology has introduced the LTC1840, a dual fan speed controller with a two-wire interface for network servers, desktop PCs or other high efficiency applications where a separate DC-DC converter drives each fan.

In these applications, the need to precisely control fan speed is required to maintain optimum operating temperature.

Switching regulators can be used to maximise efficiency when driving high power fans as opposed to linear regulators or discrete circuits.

The device includes two 8-bit DACs with full-scale output of 100 µA to sink current from the feedback nodes of DC-DC converters controlling the voltage to each fan.

The LTC1840 reads the tachometer outputs from each fan to provide feedback to the processor.

The LTC1840 simplifies the task of efficiently and precisely controlling fan speeds in network server, desktop PC or telecom environments.

The device allows the system to turn the fans on if communication is lost. The first method uses an access timer for the serial interface and a disable feature providing a failsafe setting if the bus becomes locked.

A second method uses a single-pin BLAST feature to force both fans to full speed. Additionally, four general purpose I/Os are available for driving LEDs or for other purposes.