ADT7462ACPZ-R7 datasheet(47/81 Pages) ONSEMI

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ADT7462

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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%.

Step 11—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 (0x1A)

Bits [4:2] RR1 select the ramp rate for PWM1.

000 = 1 time slot = 35 seconds

001 = 2 time slots = 17.6 seconds

010 = 3 time slots = 11.8 seconds

011 = 5 time slots = 7 seconds

100 = 8 time slots = 4.4 seconds

101 = 12 time slots = 3 seconds

110 = 24 time slots = 1.6 seconds

111 = 48 time slots = 0.8 seconds

Bits [7:5] RR2 select the ramp rate for PWM2.

000 = 1 time slot = 35 seconds

001 = 2 time slots = 17.6 seconds

010 = 3 time slots = 11.8 seconds

011 = 5 time slots = 7 seconds

100 = 8 time slots = 4.4 seconds

101 = 12 time slots = 3 seconds

110 = 24 time slots = 1.6 seconds

111 = 48 time slots = 0.8 seconds

Enhanced Acoustics Register 2 (0x1B)

Bits [4:2] RR3 select the ramp rate for PWM3.

000 = 1 time slot = 35 seconds

001 = 2 time slots = 17.6 seconds

010 = 3 time slots = 11.8 seconds

011 = 5 time slots = 7 seconds

100 = 8 time slots = 4.4 seconds

101 = 12 time slots = 3 seconds

110 = 24 time slots = 1.6 seconds

111 = 48 time slots = 0.8 seconds

Bits [7:5] RR4 select the ramp rate for PWM4.

000 = 1 time slot = 35 seconds

001 = 2 time slots = 17.6 seconds

010 = 3 time slots = 11.8 seconds

011 = 5 time slots = 7 seconds

100 = 8 time slots = 4.4 seconds

101 = 12 time slots = 3 seconds

110 = 24 time slots = 1.6 seconds

111 = 48 time slots = 0.8 seconds

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 ADT7462 into manual mode and

changing the PWM output from 0% to 100% PWM duty

cycle. The PWM output takes 35 seconds 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 seconds 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 77. Enhanced Acoustics Mode with Ramp

Rate = 48

TIME (s)

140

0.76

120

100

120

100

RTEMP (5C)

PWM CYCLE (%)

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 seconds for the fan to reach full speed.

Figure 78. Enhanced Acoustics Mode with Ramp

Rate = 8

TIME (s)

120

4.4

140

120

100

RTEMP (5C)

PWM DUTY CYCLE (%)

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