ADT7473 Analog Devices, Inc., ADT7473 Datasheet - Page 41

• Manufacturer Part Number: ADT7473
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

Programming the PWM
The PWM
maximum PWM d
a
duty cycle to be set in steps of 0.39%.
The value to be programmed into the PWM
given by
Example 1: For a maximum PWM duty cycle of 50%
Example 2: For a minimum PWM duty cycle of 75%
PWM
Register 0x38, PWM1 Maximum Duty Cycle = 0xFF
(100% default)
Register 0x39, PWM2 Maximum Duty Cycle = 0xFF
(100% default)
Register 0x3A, PWM3 Maximum Duty Cycle = 0xFF
(100% default)
See the Note on Fan Speed and PWM Duty Cycle section.
nywhere from 0% to 100%. This allows the maximum PWM
Value (decimal) = PWM
Value (decimal) – 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 80 (hex)
Value (decimal) = 75/0.39 = 85 (decimal)
Value = 192 (decimal) or C0 (hex)
MAX
PWM
Figure 52. PWM
PWM
Registers
100%
MAX
MAX
MIN
0%
registers a
Below the THERM Temperature Limit
uty cycle for each output to be co
MAX
T
Determines Maximum PWM Duty Cycle
MIN
re 8-
MAX
bit registers that allow t
MAX
Registers
/0.39
TEMPERATURE
MAX
register is
nfigured
he
Rev. A | Page 41 of 76
STEP 6: T
T
control occurs once the programmed T
exceeded. T
that is, a T
PWM
Refer to Figure 53.
The T
procedure:
1.
2.
3.
4.
Figure 54 shows how adjusting PWM
RANGE
Determine the maximum operating temperature for that
channel (for example, 70°C).
Determine experimentally the fan speed (PWM duty cycle
value) that does not exceed the temperature at the worst-
case operating points (for example, 70°C is reached when
the fans are running at 50% PWM duty cycle).
Determine the slope of the required control loop to meet
these requirements.
Gra
th
Devices representative for details.
MIN
RANGE
e ADT7473 evaluation software. Ask your local Analog
is the range of temperature over which automatic fan
PWM
phically p
100%
is increased or decreased, the effective T
50%
33%
RANGE
100%
0%
RANGE
or fan control slope is determined by the following
Figure 53. T
RANGE
MIN
0%
Figure 54. Adjusting PWM
of 40°C holds true only for PWM
is a temperature slope, not an arbitrary value,
FOR TEMPERATURE CHANNELS
rog
T
RANGE
ram and visualize this functi
MIN
T
MIN
Parameter Affects Cooling Slope
30°C
40°C
T
MIN
RANGE
TEMPERATURE
MIN
Affects T
MIN
affects T
temperature is
RANGE
MIN
RA GE
RANGE
ona
ADT7473
N
= 33%. If
lity usin
.
changes.
g