ADT7475 Analog Devices, Inc., ADT7475 Datasheet - Page 44

• Manufacturer Part Number: ADT7475
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

ADT7475
STEP 7: T
T
temperature channel. Above this temperature, a component
such as the CPU or VRM might be operating beyond its safe
operating limit. When the temperature measured exceeds
T
provide critical system cooling.
The fans remain running at 100% until the temperature drops
below T
programmed into the hysteresis registers (0x6D and 0x6E).
The default hysteresis value is 4°C.
THERM
THERM
100
100
Figure 59. T
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
, all fans drive at 100% PWM duty cycle (full speed) to
0
0
is the absolute maximum temperature allowed on a
0
0
THERM
VRM TEMPERATURE
VRM TEMPERATURE
THERM
10
10
− hysteresis, where hysteresis is the number
RANGE
20
20
FOR TEMPERATURE CHANNELS
and % Fan Speed Slopes for VRM, Ambient, and
CPU Temperature Channels
TEMPERATURE ABOVE T
AMBIENT TEMPERATURE
TEMPERATURE ABOVE T
30
30
CPU TEMPERATURE
AMBIENT TEMPERATURE
40
40
50
50
CPU TEMPERATURE
60
60
70
MIN
70
MIN
80
80
90
90
100
100
Rev. B | Page 44 of 68
The T
operating temperature of the system. Because exceeding any
T
effects. Ultimately, this limit should be set up as a fail-safe, and
the designer should ensure that it is not exceeded under normal
system operating conditions.
Note that T
speed no matter how automatic fan control settings are
configured. This allows some flexibility because a T
can be selected based on its slope, while a hard limit (such as
70°C) can be programmed as T
the fan reaches full speed) by setting T
example, 70°C).
THERM Registers
Register 0x6A, Remote 1 THERM Temperature Limit = 0x64
(100°C default)
Register 0x6B, Local THERM Temperature Limit = 0x64 (100°C
default)
Register 0x6C, Remote 2 THERM Temperature Limit = 0x64
(100°C default)
THERM Hysteresis
THERM hysteresis on a particular channel is configured via the
hysteresis settings in Register 0x6D and Register 0x6E. For
example, setting hysteresis on the Remote 1 channel also sets
the hysteresis on Remote 1 THERM .
Hysteresis Registers
Register 0x6D, Remote 1 and Local Temperature/T
Hysteresis Register.
Bits [7:4] (HYSR1), Remote 1 temperature hysteresis (4°C
default).
Bits [3:0] (HYSL), local temperature hysteresis (4°C default).
Register 0x6E, Remote 2 Temperature T
Bits [7:4] (HYSR2), Remote 2 temperature hysteresis (4°C
default).
Because each hysteresis setting is four bits, hysteresis values are
programmable from 1°C to 15°C. It is not recommended that
hysteresis values ever be programmed to 0°C because this dis-
ables hysteresis. In effect, this causes the fans to cycle (during a
THERM event) between normal speed and 100% speed or,
while operating close to T
creating unsettling acoustic noise.
THERM
THERM
limit runs all fans at 100%, it has very negative acoustic
THERM
limit should be considered the maximum worst-case
limits are nonmaskable and affect the fan
MIN
, between normal speed and off,
MAX
(the temperature at which
THERM
MIN
Hysteresis Register.
to that limit (for
MIN
RANGE
value