I2C Fan Control Ensures Continuous System Cooling
Design Note 270
Dilian Reyes
slowing down due to worn bearings or halted from a
jam will cause an overflow in the internal counter and
a corresponding bit is set low in the fault register. The
system controller can then take action, shutting down
the faulty fan and summoning maintenance. Introduction
Linear Technology’s LTC ®1840 is a dual fan speed
controller for high availability servers and other rackbased network and telecom equipment. The LTC1840
offers advanced control and monitoring capabilities,
accessed via an I2C and SMBus compatible 2-wire
serial interface. In addition to two fan speed control
channels, the LTC1840 also includes a fan tachometer and fault monitoring, nine slave addresses
and four general-purpose programmable I/O pins
in a 16-pin SSOP package. Adjusting fan speed to
match instantaneous cooling requirements increases
energy efficiency and reduces noise. By operating at
reduced speeds, fan bearings are subjected to less
wear, increasing fan life and reliability. The chip contains four general purpose input/output
(GPIO) pins that are configured independently. As opendrain outputs, they can be set high, low or to pulse at a
1.5Hz rate. The outputs are rated at 10mA sink current
for compatibility with LEDs. Conп¬Ѓgured as inputs, the …