Step 8: Thyst For Temperature Channels - Analog Devices dBCool ADT7473 Manual

100%
0%
REMOTE 2 =
CPU TEMP
LOCAL =
VRM TEMP
REMOTE 1 =
AMBIENT TEMP
STEP 8: T FOR TEMPERATURE CHANNELS
H YST
T is the amount of extra co
HYST
temperature measured has dropped back below T
fan turns off. The premise for temperature hysteresis (T
that, without it, the fan would merely chatter or cycle on a
regularly whenever temperature is hovering at about the T
setting.
The T value chosen determines the amount of time needed
HYST
for the system to cool down or heat up as the fan turns on and
off. Values of hysteresis are programmable in the range 1°C to
15°C. Larger values of T
HYST
and off. The T default value is set at 4°C.
HYS T
The T setting applies not only to the temperature hysteresis
HYST
for fan on/off, but the same setting is used for the T
hysteresis value, described in Step 6: T
Channels. Therefore, programming Register 0x6D and Register
0x6E sets the hysteresis for both fan on/off and the THERM
function.
T
RANGE
T T
MIN THERM
THERMAL CALIBRATION
100%
0%
T T
MIN RANGE
THERMAL CALIBRATION
100%
0%
T T
MIN RANGE
THERMAL CALIBRATION
100%
0%
T T
MIN RANGE
Figure 59. How T
oling a fan provides after the
before the
MIN
HYST
prevent the fans from chattering
THERM
for Temperature
RANGE
PWM
MIN
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
PW M
MI N
RAMP
CONTROL
MUX
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 2
MEASUREMENT
PWM
MIN
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 3
AND 4
MEASUREMENT
Rela tes to Automa tic Fan Control
THERM
Hysteresis Registers
Register 0x6D, Remote 1, Local Hysteresis Register
Bits [7:4] Remote 1 temperature hysteresis (4°C default)
) is
nd off
Bits [3:0] Local temperature hysteresis (4°C default)
MIN
Register 0x6E, Remote 2 Temperature Hysteresis Register
Bits [7:4], Remote 2 temperature hysteresis (4°C default)
In some applications, it is required that fans not turn off below
T , but remain running at PWM
MIN
on
Acoustics Register 1 (0x62) allow the fans to be turned off or to
be kept spinning below T
value has no effect on the fan when the temperature drops
below T .
MIN
Rev. A | Page 45 of 76
PWM
CONFIG
PWM
PWM1
GENERATOR
TACH1
PWM
CPU F AN SINK
CONFIG
PWM
PWM2
GENERATOR
TACH2
PWM
CO NFIG
FRONT CHASSIS
PWM
PWM3
GENERATOR
TACH3
REAR CHASSIS
. Bits [7:5] of the Enhance
MIN
. If the fans are always on, the T
MIN
ADT7473
HYST