ADT7490(2016) 查看數據表（PDF） - ON Semiconductor
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ADT7490 Datasheet PDF : 75 Pages
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ADT7490
Theory of Operation
The ADT7490 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 ADT7490 are
performed over the serial bus. In addition, Pin 14 can be
reconfigured as an SMBALERT output to signal
out-of-limit conditions.
Feature Comparisons Between the ADT7490 and
ADT7476A
The ADT7490 is pin and register map compatible with the
ADT7476A. The new or additional features are detailed in
the following sections.
PECI Input
CPU thermal information is provided through the PECI
input. The ADT7490 has PECI master capabilities and can
read the CPU thermal information through the PECI
interface. Each CPU address can have up to two PECI
domains. The ADT7490 has the ability to record four PECI
temperature readings corresponding to the four PECI
addresses of 0x30 to 0x33. The hotter of the two domains at
any given address is stored in the PECI value registers. A
PECI reading is a negative value, in degrees Celsius, which
represents the offset from the thermal control circuit (TCC)
activation temperature. PECI information is not converted
to absolute temperature reading. PECI information is in a
16-bit twos complement value; however, the ADT7490
records the sign bit as well as the bits from 12:6 in the 16-bit
PECI payload. See the Platform Environment Control
Interface (PECI) Specification from Intel® for more details
on the PECI data format. The PECI format is represented in
Table 6.
Table 6. PECI DATA FORMAT
MSB Upper Nibble
MSB Lower Nibble
S
x
x
x
x
x
x
x
Sign Bit
Integer Value (0°C to 127°C)
There are associated high and low limits for each PECI
reading that can be programmed. The limit values take the
same format as the PECI reading. Therefore, the
programmed limits are not absolute temperatures but a
relative offset in degrees Celsius from the TCC activation
temperature. An out-of-limit event is recorded as follows:
High Limit > Comparison Performed
Low Limit ≤ Comparison Performed
An out-of-limit event is recorded in the associated status
register and can be used to assert the SMBALERT pin.
Temperature Data REPLACE Mode
The REPLACE mode is configured by setting Bit 4 of
Register 0x36. In this mode, the data in the existing
Remote 1 registers are replaced by PECI0 data and vice
versa. This is a legacy mode that allows the thermal data
from CPU1 to be stored in the same registers as in the
ADT7476A. This reduces the software changes in systems
transitioning from CPUs with thermal diodes to CPUs with
a PECI interface. See the PECI Temperature Measurement
section for more details.
Fan Control Using PECI Information
The CPU thermal information from PECI can be used in the
existing automatic fan control algorithms. This temperature
reading remains relative to TCC activation temperature and
the associated AFC control parameters are programmed in
relative temperatures as opposed to absolute temperatures,
and are in the same format as detailed in Table 6. PECIMIN,
TRANGE, and TCONTROL are user defined.
PWM = 100%
PWMMAX
PWMMIN
PECI = 0
TRANGE
PWM = 0%
PECIMIN
(TMIN)
TCONTROL
(TMAX) TCC
Figure 17. Overview of Automatic Fan Speed Control
Using PECI Thermal Information
Dynamic TMIN Fan Control Mode
The automatic fan speed control incorporates a feature
called dynamic TMIN control. This intelligent fan control
feature reduces the design effort required to program the
automatic fan speed control loop and improves the system
acoustics.
VTT Input
The VTT voltage is monitored on Pin 8. This voltage is
also used as the reference voltage for the PECI interface. The
VTT voltage must be connected to the ADT7490 in order for
the PECI interface to be operational.
IMON Monitoring
The IMON input on Pin 19 can be used to monitor the IMON
output of ON Semiconductor’s VR10/VR11.1 controllers.
IMON is a voltage representation of the CPU current. Using
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