ADT7473_11 ONSEMI [ON Semiconductor], ADT7473_11 Datasheet - Page 50

• Manufacturer Part Number: ADT7473_11
• Description: dbCOOL Remote Thermal Monitor and Fan Control
• Manufacturer: ONSEMI [ON Semiconductor]

Effect of Ramp Rate on Enhanced Acoustics Mode
the PWM drive frequency, f, because T = 1/f. For a given
PWM period, T, the PWM period is subdivided into 255
equal time slots. One time slot corresponds to the smallest
possible increment in the PWM duty cycle. A PWM signal
of 33% duty cycle is, therefore, high for 1/3 x 255 time slots
and low for 2/3 x 255 time slots. Therefore, a 33% PWM
duty cycle corresponds to a signal that is high for 85 time
slots and low for 170 time slots.
selectable from the values 1, 2, 3, 5, 8, 12, 24, and 48. The
ramp rates are discrete time slots. For example, if the ramp
rate is 8, then eight time slots are added to the PWM high duty
cycle each time the PWM duty cycle needs to be increased.
If the PWM duty cycle value needs to be decreased, it is
decreased by eight time slots. Figure 76 shows how the
enhanced acoustics mode algorithm operates.
PWM duty cycle based on the temperature measured. If the
new PWM duty cycle value is greater than the previous
PWM value, then the previous PWM duty cycle value is
incremented by either 1, 2, 3, 5, 8, 12, 24, or 48 time slots,
depending on the settings of the enhanced acoustics
registers. If the new PWM duty cycle value is less than the
previous PWM value, the previous PWM duty cycle is
decremented by 1, 2, 3, 5, 8, 12, 24, or 48 time slots. Each
time the PWM duty cycle is incremented or decremented, its
value is stored as the previous PWM duty cycle for the next
comparison. A ramp rate of 1 corresponds to one time slot,
which is 1/255 of the PWM period. In enhanced acoustics
mode, incrementing or decrementing by 1 changes the PWM
output by 1/255 x 100%.
The PWM signal driving the fan has a period, T, given by
The ramp rates in the enhanced acoustics mode are
The enhanced acoustics mode algorithm calculates a new
PWM_OUT
33% DUTY
Figure 75. 33% PWM Duty Cycle Represented
CYCLE
TIME SLOTS
85
in Time Slots
= 255 TIME SLOTS
PWM OUTPUT
(ONE PERIOD)
TIME SLOTS
170
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50
Step 12: Ramp Rate for Acoustic Enhancement
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 (0x62)
Bits [2:0] ACOU, select the ramp rate for PWM1.
Enhanced Acoustics Register 2 (0x63)
Bits [2:0] ACOU3, select the ramp rate for PWM3.
Bits [6:4] ACOU2, select the ramp rate for PWM2.
The optimal ramp rate for acoustic enhancement can be
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
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
Figure 76. Enhanced Acoustics Algorithm
TEMPERATURE
BY RAMP RATE
DUTY CYCLE
IS NEW PWM
PWM VALUE
CALCULATE
INCREMENT
PREVIOUS
PREVIOUS
NEW PWM
VALUE >
VALUE?
READ
YES
NO
BY RAMP RATE
DECREMENT
PWM VALUE
PREVIOUS