ADT7460 Analog Devices, Inc., ADT7460 Datasheet - Page 19

• Manufacturer Part Number: ADT7460
• Description: Dbcool? Remote Thermal Controller And Fan Controller
• Manufacturer: Analog Devices, Inc.

Nulling Out Temperature Errors
As CPUs run faster, it becomes more difficult to avoid high
frequency clocks when routing the D+, D− traces around a
system board. Even when recommended layout guidelines are
followed, there may still be temperature errors attributed to
noise being coupled onto the D+/D− lines. High frequency
noise generally has the effect of giving temperature measure-
ments that are too high by a constant amount. The ADT7460
has temperature offset registers at Addresses 0x70, 0x72 for the
Remote 1 and Remote 2 temperature channels. By doing a one-
time calibration of the system, one can determine the offset
caused by system board noise and null it out using the offset
registers. The offset registers automatically add a twos
complement 8-bit reading to every temperature measurement.
The LSB adds 0.25°C offset to the temperature reading so the
8-bit register effectively allows temperature offsets of up to
±32°C with a resolution of 0.25°C. This ensures that the
readings in the temperature measurement registers are as
accurate as possible.
Table 15. Temperature Offset Registers
Register
0x70
0x71
0x72
Temperature Measurement Limit Registers
Associated with each temperature measurement channel are
high and low limit registers. Exceeding the programmed high or
low limit causes the appropriate status bit to be set. Exceeding
either limit can also generate SMBALERT interrupts.
Table 16. Temperature Measurement Limit Registers
Register
0x4E
0x4F
0x50
0x51
0x52
0x53
Overtemperature Events
Overtemperature events on any of the temperature channels can
be detected and dealt with automatically in automatic fan speed
control mode. Registers 0x6A to 0x6C are the THERM limits.
When a temperature exceeds its THERM limit, all fans run at
100% duty cycle. The fans continue running at 100% until the
temperature drops below THERM – Hysteresis. (This can be
disabled by setting the BOOST bit in Configuration Register 3,
Bit 2, Register 0x78). The hysteresis value for that THERM limit
is the value programmed into Registers 0x6D and 0x6E
(hysteresis registers). The default hysteresis value is 4°C.
Description
Remote 1 temperature low limit
Remote 1 temperature high limit
Local temperature low limit
Local temperature high limit
Remote 2 temperature low limit
Remote 2 temperature high limit
Description
Remote 1 temperature offset
Local temperature offset
Remote 2 temperature offset
Default
0x00 (0°C)
0x00 (0°C)
0x00 (0°C)
Default
0x81
0x7F
0x81
0x7F
0x81
0x7F
Rev. C | Page 19 of 52
ADDITIONAL ADC FUNCTIONS FOR
TEMPERATURE MEASUREMENT
A number of other functions are available on the ADT7460 to
offer the systems designer increased flexibility:
Turn-Off Averaging
For each temperature measurement read from a value register,
16 readings have actually been made internally and the results
averaged before being placed into the value register. Sometimes
it may be necessary to take a very fast measurement, for
example, of CPU temperature. Setting Bit 4 of Configurat
Register 2 (Re
every 15.5 ms. Each remote temperature measurem
4 ms and the local temperature measurement take
Singl
Settin
A
m
channel only. The appropriate ADC channel is selected b
to B
(Reg. 0 55).
Table
Bit
<4>
<6>
Table 18. TACH1 Minimum High Byte (Reg. 0x55)
B
<7:5>
THERM LIMIT
it
FANS
DT7460 into single-channel ADC conversion mode. In this
ode, the ADT7460 can be made to read a single temperature
its <
TEMPERATURE
e-Ch
g Bit
17
x
7:5> of the TA
Description
Selects ADC channel for single-channel convert mode
Value
101
110
111
. Conf
annel ADC Con
6 of Configuration Register 2 (R
Description
1: Averaging off
1: single-channel convert mode
g. 0x73) turns averaging off. This takes a reading
iguration Register 2 (
Figure 28. THERM Limit Operation
CH1 minimum high byte register
100%
versions
Reg. 0x73)
Channel Selected
Remote 1 temp
Local temp
Remote 2 temp
HYSTERESIS = (°C)
eg. 0x73) places the
s 1.4 ms.
ADT7460
ent takes
y writing
ion