ADT7460
Product Description
The ADT7460 is a thermal monitor and multiple fan
controller for any system requiring monitoring and cooling.
The device communicates with the system via a serial
System Management Bus (SMBus). The serial bus
controller has an optional address line for device selection
(Pin 9), a serial data line for reading and writing addresses
and data (Pin 16), and an input line for the serial clock
(Pin 1). All control and programming functions of the
ADT7460 are performed over the serial bus. In addition, two
of the pins can be reconfigured as an SMBALERT output to
indicate out−of−limit conditions.
Measurement Inputs
The ADC also accepts input from an on−chip band gap
temperature sensor, which monitors system ambient
temperature.
Sequential Measurement
When the ADT7460 monitoring sequence is started, it
cycles sequentially through the measurement of 2.5 V input
and the temperature sensors. Measured values from these
inputs are stored in value registers. These can be read out
over the serial bus or can be compared with programmed
limits stored in the limit registers. The results of
out−of−limit comparisons are stored in the status registers,
which can be read over the serial bus to flag out−of−limit
conditions.
Recommended Implementation
The device has three measurement inputs, one for voltage
and two for temperature. It can also measure its own supply
voltage and can measure ambient temperature with its
on−chip temperature sensor.
Pin 14 is an analog input with an on−chip attenuator and
is configured to monitor 2.5 V.
Power is supplied to the chip via Pin 3, and the system also
monitors V
CC
through this pin. In PCs, this pin is normally
connected to a 3.3 V standby supply. This pin can, however,
be connected to a 5.0 V supply and monitor it without
over−ranging.
Remote temperature sensing is provided by the D1± and
D2± inputs, to which diode−connected, external
temperature−sensing transistors, such as a 2N3904 or CPU
thermal diode, may be connected.
Configuring the ADT7460 as in Figure 12 allows the
systems designer the following features:
♦
Two PWM outputs for fan control of up to three
fans (the front and rear chassis fans are connected in
parallel).
♦
Three TACH fan speed measurement inputs.
♦
V
CC
measured internally through Pin 3.
♦
CPU temperature measured using Remote 1
temperature channel.
♦
Ambient temperature measured through Remote 2
temperature channel.
♦
Bidirectional THERM pin. Allows Intel Pentium 4
PROCHOT monitoring and can function as an
overtemperature THERM output.
♦
SMBALERT system interrupt output.
ADT7460
FRONT
CHASSIS
FAN
PWM1
TACH2
TACH1
CPU FAN
REAR
CHASSIS
FAN
PWM3
TACH3
D2+
D2–
THERM
PROCHOT
CPU
AMBIENT
TEMPERATURE
D1+
D1–
SDA
SCL
SMBALERT
GND
ICH
Figure 12. Recommended Implementation
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