ADT7468 Analog Devices, Inc., ADT7468 Datasheet - Page 57

• Manufacturer Part Number: ADT7468
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

R2T = 0, disables dynamic T
is not adjusted and the channel behaves as described in the
Automatic Fan Control Overview section.
<6> LT = 1, enables dynamic T
erature channel. The chosen T
based on the current temperature, operating point, and high
and low limits for this zone.
LT = 0, disables dynamic T
not adjusted and the channel behaves as described in the
Automatic Fan Control Overview section.
<7> R1T = 1, enables dynamic T
temperature channel. The chosen T
adjusted based on the current temperature, operating point, and
high and low limits for this zone.
R1T = 0, disables dynamic T
is not adjusted and the channel behaves as described in the
Automatic Fan Control Overview section.
STEP 12: RAMP RATE FOR ACOUSTIC
ENHANCEMENT
The optimal ramp rate for acoustic enhancement can be found
through system characterization after the thermal optimization
has been finished. The effect of each ramp rate should be
logged, if possible, to determine the best setting for a given
solution.
Enhanced Acoustics Register 1 (Reg. 0x62)
<2:0> ACOU, selects the ramp rate for PWM1.
Enhance Acoustics Register 2 (Reg. 0x63)
<2:0> ACOU3, selects the ramp rate for PWM3.
000 = 1 time slot = 35 sec
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
101 = 12 time slots =3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
000 = 1 time slot = 35 sec
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
101 = 12 time slots = 3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
MIN
MIN
MIN
MIN
control. The T
MIN
control. The T
control. The T
MIN
value is dynamically adjusted
control on the local temp-
MIN
control on the Remote 1
value is dynamically
MIN
MIN
MIN
value chosen is
value chosen
value chosen
Rev. A | Page 57 of 84
<6:4> ACOU2, selects the ramp rate for PWM2.
Another way to view the ramp rates is to measure the time it
takes for the PWM output to ramp up from 0% to 100% duty
cycle for an instantaneous change in temperature. This can be
tested by putting the ADT7468 into manual mode and changing
the PWM output from 0% to 100% PWM duty cycle. The PWM
output takes 35 secs to reach 100%, when a ramp rate of one
time slot is selected.
Figure 77 shows remote temperature plotted against PWM duty
cycle for enhanced acoustics mode. The ramp rate is set to 48,
which corresponds to the fastest ramp rate. Assume that a new
temperature reading is available every 115 ms. With these
settings, it takes approximately 0.76 secs to go from 33% duty
cycle to 100% duty cycle (full speed). Even though the
temperature increases very rapidly, the fan ramps up to full
speed gradually.
Figure 78 shows how changing the ramp rate from 48 to 8
affects the control loop. The overall response of the fan is
slower. Because the ramp rate is reduced, it takes longer for the
fan to achieve full running speed. In this case, it takes
approximately 4.4 sec for the fan to reach full speed.
000 = 1 time slot = 35 sec
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
101 = 12 time slots = 3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
140
120
100
80
60
40
20
Figure 77. Enhanced Acoustics Mode with Ramp Rate = 48
0
0
R
TEMP
(°C)
PWM CYCLE (%)
TIME (s)
0.76
ADT7468
120
100
80
60
40
20
0