EVAL-ADT7475EB ON Semiconductor, EVAL-ADT7475EB Datasheet - Page 37

• Manufacturer Part Number: EVAL-ADT7475EB
• Description: BOARD EVALUATION FOR ADT7475
• Manufacturer: ON Semiconductor
• Series: dBCool®r
• Type: Temperature Sensorr

Specifications of EVAL-ADT7475EB

• Contents: Evaluation Board
• For Use With/related Products: ADT7475
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Ambient temperature drives the front chassis fan and rear
chassis fan connected to PWM2 and PWM3. The front
chassis fan is configured to run at PWM
chassis fan is configured to run at PWM
CPU fan is configured to run at PWM
than that for 3−wire fans. In many cases, 4−wire fans can
start with a PWM drive of as little as 20% or less. In extreme
cases, some 3−wire fans do not run unless a PWM drive of
60% or more is applied.
Step 7: T
on a 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
duty cycle (full speed) to provide critical system cooling.
drops below T
Figure 58. T
Note that the control range for 4−wire fans is much wider
T
The fans remain running at 100% until the temperature
THERM
100
100
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
Ambient, and CPU Temperature Channels
0
0
0
0
VRM TEMPERATURE
VRM TEMPERATURE
THERM
is the absolute maximum temperature allowed
10
10
RANGE
THERM
for Temperature Channels
20
20
THERM
and % Fan Speed Slopes for VRM,
TEMPERATURE ABOVE T
AMBIENT TEMPERATURE
TEMPERATURE ABOVE T
30
30
− hysteresis, where hysteresis is the
CPU TEMPERATURE
AMBIENT TEMPERATURE
40
40
, all fans drive at 100% PWM
50
50
CPU TEMPERATURE
60
60
MIN
MIN
MIN
70
70
MIN
MIN
= 10%.
= 20%. The rear
80
80
= 30%. The
90
90
http://onsemi.com
100
100
37
number programmed into the hysteresis registers (0x6D and
0x6E). The default hysteresis value is 4°C.
worst−case operating temperature of the system. Because
exceeding any T
very negative acoustic 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.
fan speed no matter how automatic fan control settings are
configured. This allows some flexibility because a T
value can be selected based on its slope, while a hard limit
(such as 70°C) can be programmed as T
temperature at which the fan reaches full speed) by setting
T
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
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
Register
Bits [7:4] (HYSR2), Remote 2 Temperature Hysteresis
(4°C default)
values are programmable from 1°C to 15°C. It is not
recommended that hysteresis values ever be programmed to
0°C because this disables 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
between normal speed and off, creating unsettling acoustic
noise.
THERM
The T
Note that T
THERM hysteresis on a particular channel is configured
Because each hysteresis setting is four bits, hysteresis
THERM
to that limit (for example, 70°C).
THERM
limit should be considered the maximum
THERM
limits are non−maskable and affect the
limit runs all fans at 100%, it has
MIN
Hysteresis
MAX
RANGE
MIN
(the
MIN
,