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ADT7460
FUNCTIONAL DESCRIPTION
General 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. 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 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 tem-
perature 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 V supply and monitor it without overranging.
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.
The ADC also accepts input from an on-chip band gap tem-
perature sensor that 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.
ADT7460 Address Selection
Pin 8 is the dual function PWM3/
ADDRESS ENABLE
pin.
If Pin 8 is pulled low on power-up, the ADT7460 will read the
state of Pin 9 (TACH4/ADDRESS SELECT/
THERM
pin) to
determine the ADT7460’s slave address. If Pin 8 is high on
power-up, then the ADT7460 will default to SMBus slave
address 0x2E. This function is described in more detail later.
INTERNAL REGISTERS OF THE ADT7460
A brief description of the ADT7460’s principal internal regis-
ters is given below. More detailed information on the function
of each register is given in Tables IV to XLI.
Configuration Registers
The Configuration registers provide control and configuration
of the ADT7460, including alternate pinout functionality.
Address Pointer Register
This register contains the address that selects one of the other
internal registers. When writing to the ADT7460, the first byte
of data is always a register address, which is written to the
Address Pointer Register.
Status Registers
These registers provide the status of each limit comparison and
are used to signal out-of-limit conditions on the temperature,
voltage, or fan speed channels. If Pin 14 is configured as
SMBALERT
, then this pin will assert low whenever an unmasked
status bit gets set.
Interrupt Mask Registers
These registers allow each interrupt status event to be masked
when Pin 14 is configured as an
SMBALERT
output.
Value and Limit Registers
The results of analog voltage input, temperature, and fan
speed measurements are stored in these registers, along with
their limit values.
Offset Registers
These registers allow each temperature channel reading to be
offset by a twos complement value written to these registers.
T
MIN
Registers
These registers program the starting temperature for each fan
under Automatic Fan Speed Control.
T
RANGE
Registers
These registers program the temperature-to-fan speed control
slope in Automatic Fan Speed Control mode for each PWM output.
Operating Point Registers
These registers define the target operating temperatures for each
thermal zone when running under dynamic T
MIN
control. This
function allows the cooling solution to adjust dynamically in
response to measured temperature and system performance.
Enhance Acoustics Registers
These registers allow each PWM output controlling fan to be
tweaked to enhance the system’s acoustics.