ADT7476ARQZ ON Semiconductor, ADT7476ARQZ Datasheet - Page 31

• Manufacturer Part Number: ADT7476ARQZ
• Description: IC REMOTE THERMAL CTRLR 24QSOP
• Manufacturer: ON Semiconductor
• Series: dBCool®r

Specifications of ADT7476ARQZ

• Function: Fan Control, Temp Monitor
• Topology: ADC, Comparator, Fan Speed Counter, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: SMBus™
• Output Alarm: No
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 3.6 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 24-QSOP
• Full Temp Accuracy: +/- 0.5 C
• Digital Output - Bus Interface: Serial (3-Wire, 4-Wire)
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Programming T
PWM. For the ADT7467, ADT7468 and ADT7473, T
is effectively a slope. For the ADT7475 andADT7476,
T
region where the PWM output linearly ramps from PWM
to 100% PWM.
Programming the Automatic Fan Speed Control Loop
efficiently, it is recommended to use the ADT7476
evaluation board and software while reading this section.
understanding of the automatic fan control loop and
provides step−by−step guidance on effectively evaluating
and selecting critical system parameters. To optimize the
system characteristics, the designer needs to give some
thought to system configuration, including the number of
fans, where they are located, and what temperatures are
being measured in the particular system.
the system thermal characterization should also be involved
at the beginning of the system development process.
Manual Fan Control Overview
control the speed of the fans. Because the ADT7476 has an
SMBus interface, a system can read back all necessary
voltage, fan speed, and temperature information, and use
this information to control the speed of the fans by writing
to the PWM current duty cycle register (0x30, 0x31, and
0x32) of the appropriate fan. Bits [7:5] of the PWMx
configuration registers (0x5C, 0x5D, 0x5E) are used to set
fans up for manual control.
RANGE
T
To understand the automatic fan speed control loop more
This section provides the system designer with an
The mechanical or thermal engineer who is tasked with
In unusual circumstances, it can be necessary to manually
RANGE
PWM = 100%
PWM = 0%
PWM
PWM
is no longer a slope, but defines the temperature
defines the distance between T
MAX
MIN
RANGE
Figure 46. T
T
MIN
T
RANGE
RANGE
MIN
and 100%
RANGE
http://onsemi.com
MIN
31
THERM Operation in Manual Mode
programmed THERM temperature limit, the fans
automatically speed up to maximum PWM or 100% PWM,
whichever way the appropriate fan channel is configured.
Automatic Fan Control Overview
based on the measured temperature. This is done
independently of CPU intervention once initial parameters
are set up.
remote temperature channels that can be connected to a CPU
on−chip thermal diode (available on Intel Pentium class and
other CPUs). These three temperature channels can be used
as the basis for automatic fan speed control to drive fans
using pulse−width modulation (PWM).
optimizing fan speed according to accurately measured
temperature. Reducing fan speed can also decrease system
current consumption. The automatic fan speed control mode
is very flexible due to the number of programmable
parameters, including T
T
a given fan, are critical, because they define the thermal
characteristics of the system. The thermal validation of the
system is one of the most important steps in the design
process, so these values should be selected carefully.
control circuitry on the ADT7476. From a systems level
perspective, up to three system temperatures can be
monitored and used to control three PWM outputs. The three
PWM outputs can be used to control up to four fans. The
ADT7476 allows the speed of four fans to be monitored.
Each temperature channel has a thermal calibration block,
allowing the designer to individually configure the thermal
characteristics of each temperature channel. For example,
designers can decide to run the CPU fan when CPU
temperature increases above 60°C and a chassis fan when
the local temperature increases above 45°C.
calibration settings to a particular fan drive (PWM) channel.
The right side of Figure 47 shows fan−specific controls. The
designer has individual control over parameters such as
minimum PWM duty cycle, fan speed failure thresholds,
and even ramp control of the PWM outputs. Automatic fan
control, then, ultimately allows graceful fan speed changes
that are less perceptible to the system user.
RANGE
In manual mode, if the temperature increases above the
The ADT7476 can automatically control the speed of fans
The ADT7476 has a local temperature sensor and two
Automatic fan speed control reduces acoustic noise by
Figure 47 gives a top level overview of the automatic fan
At this stage, the designer has not assigned these thermal
values for a temperature channel and, therefore, for
MIN
and T
RANGE
. The T
MIN
and