EVAL-ADT7490EBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-ADT7490EBZ' PDF : 76 Pages View PDF
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 informa-
tion 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 xxx
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 Celcius
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
TCC
PWM = 0%
PECIMIN
(TMIN)
(TMAX)
TCONTROL
Figure 18. 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 the Analog Devices ADP319x family of VR10/VR11
controllers. IMON is a voltage representation of the CPU current.
Using the IMON value and the measured VCCP value on Pin 23, the
CPU power consumption may be calculated. See the appropriate
Analog Devices flex mode data sheet for calculations. The IMON
information can be considered as an early indication of an
increase in CPU temperature.
Rev. 0 | Page 12 of 76
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