adm1027 Analog Devices, Inc., adm1027 Datasheet - Page 37

• Manufacturer Part Number: adm1027
• Description: Dbcool? Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

Enabling Acoustic Enhancement for Each PWM Output
ENHANCED ACOUSTICS REGISTER 1 (Reg. 0x62)
<3> = 1 enables acoustic enhancement on PWM1 output.
ENHANCED 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 incre-
ment in PWM duty cycle. A PWM signal of 33% duty cycle will
thus be high for 1/3
time slots. Therefore, 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 enhanced acoustics mode are selectable
between 1, 2, 3, 5, 8, 12, 24, and 48. The ramp rates are actu-
ally 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 39 shows how the enhanced acoustics
mode algorithm operates.
REV. A
Figure 38. 33% PWM Duty Cycle Represented in Time Slots
PWM_OUT
33% DUTY
CYCLE
TIME SLOTS
85
255 time slots and low for 2/3
= 255 TIME SLOTS
(ONE PERIOD)
PWM OUTPUT
TIME SLOTS
170
255
–37–
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 enhanced acoustics registers). If the new PWM
duty cycle value is less than the previous PWM value, then 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
It is important to note that when using the enhanced acoustics
mode, the fan spin-up should be disabled.
Figure 39. Enhanced Acoustics Algorithm
TEMPERATURE
IS NEW PWM
DUTY CYCLE
CALCULATE
PREVIOUS
PWM VALUE
INCREMENT
NEW PWM
PREVIOUS
VALUE >
VALUE?
BY RAMP
READ
RATE
YES
NO
DECREMENT
PWM VALUE
PREVIOUS
BY RAMP
RATE
ADM1027
100%.