ADT7463 Analog Devices, ADT7463 Datasheet - Page 24

• Manufacturer Part Number: ADT7463
• Description: Dbcool Thermal Management Controller And Voltage Monitor
• Manufacturer: Analog Devices

AN-613
smoothly to its newly calculated speed. If the tempera-
ture starts to drop, the PWM duty cycle immediately
decreases by 6% every update. So the fan ramps
smoothly up or down without inherent system delay.
Consider controlling the same CPU cooler fan (on
PWM1) and chassis fan (on PWM2) using Remote 1 tem-
perature. The T
been defined in automatic fan speed control mode, i.e.,
thermal characterization of the control loop has been
optimized. Now the chassis fan is noisier than the CPU
cooling fan. So PWM2 can be placed into acoustic
enhancement mode independently of PWM1. The
acoustics of the chassis fan can therefore be adjusted
without affecting the acoustic behavior of the CPU cooling
fan, even though both fans are being controlled by
Remote 1 temperature. This is exactly how acoustic
enhancement works on the ADT7460/ADT7463.
ENABLING ACOUSTIC ENHANCEMENT FOR EACH PWM
OUTPUT
ENHANCE ACOUSTICS REGISTER 1 (Reg. 0x62)
<3> = 1 Enables acoustic enhancement on PWM1 output.
ENHANCE ACOUSTICS REGISTER 2 (Reg. 0x63)
<7> = 1 Enables acoustic enhancement on PWM2 output.
<3> = 1 Enables acoustic enhancement on PWM3 output.
EFFECT OF RAMP RATE ON ENHANCED ACOUSTICS
MODE
The PWM signal driving the fan will have a period, T,
given by the PWM drive frequency, f, since 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 PWM duty cycle. A PWM
signal of 33% duty cycle will thus be high for 1/3
time slots and low for 2/3
33% PWM duty cycle corresponds to a signal that is high
for 85 time slots and low for 170 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 actually discrete time slots. For example,
if the ramp rate = 8, then eight time slots will be 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 will be decreased by eight time
slots. Figure 31 shows how the enhanced acoustics
mode algorithm operates.
PWM_OUT
33% DUTY
Figure 30. 33% PWM Duty Cycle Represented in
Time Slots
CYCLE
TIME SLOTS
MIN
85
and T
= 255 TIME SLOTS
(ONE PERIOD)
PWM OUTPUT
RANGE
255 time slots. Therefore,
TIME SLOTS
settings have already
170
255
–24–
The enhanced acoustics mode algorithm calculates a
new PWM duty cycle based on the temperature mea-
sured. If the new PWM duty cycle value is greater than
the previous PWM value, 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, it 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
STEP 11: DETERMINING THE 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.
ENHANCE ACOUSTICS REGISTER 1 (Reg. 0x62)
<2:0> ACOU Select the Ramp Rate for PWM1.
Figure 31. Enhanced Acoustics Algorithm
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
TEMPERATURE
IS NEW PWM
DUTY CYCLE
CALCULATE
INCREMENT
PWM VALUE
100%.
PREVIOUS
PREVIOUS
NEW PWM
VALUE >
BY RAMP
VALUE?
READ
RATE
YES
NO
DECREMENT
PWM VALUE
PREVIOUS
BY RAMP
RATE
REV. 0