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Product Description
The ADT7476A is a complete thermal monitor and
multiple fan controller for any system requiring thermal
monitoring and cooling. The device communicates with the
system via a serial system management bus. The serial bus
controller has a serial data line for reading and writing
addresses and data (Pin 1), and an input line for the serial
clock (Pin 2). All control and programming functions for the
ADT7476A are performed over the serial bus. In addition,
a pin can be reconfigured as an SMBALERT output to signal
out-of-limit conditions.
Feature Comparisons Between ADT7476A
and ADT7468
•
Dynamic T
MIN
associated registers are no longer available in the
ADT7476A. The following related registers are gone:
♦
Calibration Control 1 (0x36)
♦
Calibration Control 2 (0x37)
♦
Operating Point (0x33, 0x34, and 0x35)
•
Previously (in the ADT7468), T
of the automatic fan control algorithm. T
defines a true temperature range (in the ADT7476A).
•
Acoustic filtering is now assigned to temperature zones,
not to fans. Available smoothing times have been
increased for better acoustic performance.
•
Temperature measurements are now made with two
switching currents instead of three. SRC is not available
in the ADT7476A.
•
High frequency PWM can now be enabled/disabled on
each PWM output individually.
•
THERM can now be enabled/disabled on each
temperature channel individually.
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, dynamic operating point, and
defined the slope
RANGE
RANGE
FRONT
CHASSIS
FAN
REAR
CHASSIS
FAN
AMBIENT
TEMPERATURE
Figure 13. ADT7476A Configuration
ADT7476A
•
The ADT7476A does not support full shutdown mode.
•
The ADT7476A offers increased temperature accuracy
on all temperature channels.
•
The ADT7476A defaults to twos complement
temperature measurement mode.
•
Some pins have swapped/added functions.
•
The powerup routine for the ADT7476A is simplified.
•
The ADT7476A has a higher maximum input voltage
TACH/PWM spec, supporting a wider range of fans.
•
V
CORE_LOW_ENABLE
Configuration Register 1 (0x40).
Recommended Implementation
Configuring the ADT7476A as shown in Figure 13 allows
the system designer to use 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
measured internally through Pin 4.
CC
now
•
CPU temperature measured using Remote 1
temperature channel.
•
Remote temperature zone measured through Remote 2
temperature channel.
•
Local temperature zone measured through the internal
temperature channel.
•
Bidirectional THERM pin. This feature allows
®
Intel
Pentium
function as an overtemperature THERM output. It can
alternatively be programmed as an SMBALERT system
interrupt output.
ADT7476A
PWM1
TACH2
TACH1
PWM3
VID[0:4]/VID[0:5]
TACH3
D2+
D2−
THERM
D1+
PROCHOT
D1−
SDA
V
CC
SCL
+5V
IN
+12V
/VID5
SMBALERT
IN
GND
www.onsemi.com
8
has been reallocated to Bit 7 of
®
4 PROCHOT monitoring and can
5(VRM9)/6(VRM10)
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