adm1027 Analog Devices, Inc., adm1027 Datasheet - Page 35

• Manufacturer Part Number: adm1027
• Description: Dbcool? Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

Step 7
Determine T
T
measured temperature has dropped back below T
fan turns off. The premise for temperature hysteresis (T
is that without it, the fan would merely chatter, or cycle on and
off regularly, whenever the temperature is hovering about the
T
The T
needed for the system to cool down or heat up, as the fan is
turning on and off. Values of hysteresis are programmable in
the range 1∞C to 15∞C. Larger values of T
chattering on and off as previously described. The T
value is 4∞C.
Hysteresis Registers
Reg. 0x6D Remote 1, Local Hysteresis Register
<7:4> = Remote 1 temperature hysteresis (default = 4∞C)
<3:0> = Local temperature hysteresis (default = 4∞C)
Reg. 0x6E Remote 2 Temperature Hysteresis Register
<7:4> = Remote 2 temperature hysteresis (default = 4∞C)
REV. A
HYST
MIN
setting.
HYST
is the amount of extra cooling a fan provides after the
value chosen will determine the amount of time
HYST
AMBIENT TEMP
REMOTE 2 =
REMOTE 1 =
VRM TEMP
CPU TEMP
for Each Temperature Channel
100%
LOCAL =
0%
Figure 36. The T
T
HYST
T
MIN
T
T
T
MIN
MIN
MIN
THERMAL CALIBRATION
THERMAL CALIBRATION
THERMAL CALIBRATION
HYST
T
RANGE
T
T
T
HYST
RANGE
RANGE
RANGE
Value Applies to Fan On/Off Hysteresis and THERM Hysteresis
T
THERM
prevent the fans
100%
100%
0%
100%
0%
0%
MIN
HYST
before the
default
HYST
MUX
)
–35–
PWM
PWM
PWM
MIN
MIN
MIN
Note that in some applications it is required that the fans not
turn off below T
of Enhance Acoustics Register 1 (Reg. 0x62) allow the fans to
be turned off or kept spinning below T
on, the T
ture drops below T
Enhance Acoustics Register 1 (Reg. 0x62)
Bit 7 (MIN3) = 0, PWM3 is OFF (0% PWM duty cycle) when
temperature is below T
Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty cycle
below T
Bit 6 (MIN2) = 0, PWM2 is OFF (0% PWM duty cycle) when
temperature is below T
Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty cycle
below T
Bit 5 (MIN1) = 0, PWM1 is OFF (0% PWM duty cycle) when
temperature is below T
Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty cycle
below T
TACHOMETERS 3
MEASUREMENT
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
ENHANCEMENT)
TACHOMETER 2
MEASUREMENT
ENHANCEMENT)
(ACOUSTIC
(ACOUSTIC
(ACOUSTIC
CONTROL
CONTROL
CONTROL
MIN
MIN
MIN
AND 4
RAMP
RAMP
RAMP
HYST
– T
– T
– T
value has no effect on the fan when the tempera-
HYST
HYST
HYST
MIN
MIN
GENERATOR
GENERATOR
GENERATOR
, but remain running at PWM
.
.
.
CONFIG
CONFIG
CONFIG
PWM
PWM
PWM
PWM
PWM
PWM
.
MIN
MIN
MIN
– T
– T
– T
HYST
HYST
HYST
PWM1
TACH1
PWM2
TACH2
PWM3
TACH3
.
.
.
MIN
. If the fans are always
ADM1027
MIN
. Bits <7:5>
CPU
FANSINK
FRONT
CHASSIS
REAR
CHASSIS