Table of Contents
Advertisement
PWM_OUT
33% DUTY
CYCLE
85
TIME SLOTS
PWM OUTPUT
(ONE PERIOD)
= 255 TIME SLOTS
Figure 72. 33% PWM Duty Cycle Represented in Time Slots
The ramp rates in the enhanced acoustics mode are 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 73 shows how the enhanced acoustics mode algorithm
operates.
READ
TEMPERATURE
CALCULATE
NEW PWM
DUTY CYCLE
IS NEW PWM
VALUE >
PREVIOUS
VALUE?
YES
INCREMENT
PREVIOUS
PWM VALUE
BY RAMP RATE
Figure 73. Enhanced Acoustics Algorithm
The enhanced acoustics mode algorithm calculates a new 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 enhance 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 × 100%.
170
TIME SLOTS
DECREMENT
NO
PREVIOUS
PWM VALUE
BY RAMP RATE
Rev. 0 | Page 53 of 76
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.
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
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
<6:4> ACOU2, selects the ramp rate for PWM2.
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
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 ADT7473 into manual mode and changing
the PWM output from 0% to 100% PWM duty cycle. The PWM
output takes 35 sec to reach 100% when a ramp rate of 1 time
slot is selected.
ADT7473
Advertisement
Table of Contents
