参数资料
| 型号： | ADT7468ZEVB |
| 厂商： | ON Semiconductor |
| 文件页数： | 57/81页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL FOR ADT7468 |
| 标准包装： | 1 |
| 其它名称： | EVAL-ADT7468EB EVAL-ADT7468EB-ND |
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ADT7468
STEP 12: RAMP RATE FOR ACOUSTIC
ENHANCEMENT
The optimal ramp rate for acoustic enhancement can be found
through system characterization after the thermal optimization
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.
has been finished. The effect of each ramp rate should be
logged, if possible, to determine the best setting for a given
140
120
R TEMP (°C)
120
100
solution.
Enhanced Acoustics Register 1 (Reg. 0x62)
100
80
<2:0> ACOU, selects the ramp rate for PWM1.
000 = 1 time slot = 35 sec
80
60
60
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
40
20
PWM CYCLE (%)
40
20
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
0
0
TIME (s)
0
0.76
101 = 12 time slots =3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
Enhance Acoustics Register 2 (Reg. 0x63)
<2:0> ACOU3, selects the ramp rate for PWM3.
000 = 1 time slot = 35 sec
Figure 77. Enhanced Acoustics Mode with Ramp Rate = 48
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.
001 = 2 time slots = 17.6 sec
120
140
010 = 3 time slots = 11.8 sec
100
R TEMP (°C)
120
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
80
60
40
PWM DUTY CYCLE (%)
100
80
60
40
<6:4> ACOU2, selects the ramp rate for PWM2.
000 = 1 time slot = 35 sec
20
20
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
0
0
TIME (s)
4.4
0
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
Figure 78. Enhanced Acoustics Mode with Ramp Rate = 8
Figure 79 shows the PWM output response for a ramp rate of 2.
In this instance, the fan took about 17.6 sec to reach full
running speed.
111 = 48 time slots = 0.8 sec
140
120
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
120
100
80
60
R TEMP (°C)
PWM DUTY CYCLE (%)
100
80
60
output takes 35 secs to reach 100%, when a ramp rate of one
time slot is selected.
40
40
Figure 77 shows remote temperature plotted against PWM duty
20
20
cycle for enhanced acoustics mode. The ramp rate is set to 48,
which corresponds to the fastest ramp rate. Assume that a new
0
0
TIME (s)
17.6
0
temperature reading is available every 115 ms. With these
Figure 79. Enhanced Acoustics Mode with Ramp Rate = 2
Rev. 3 | Page 57 of 81 | www.onsemi.com
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