ADT7475 Analog Devices, Inc., ADT7475 Datasheet - Page 41

• Manufacturer Part Number: ADT7475
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

Figure 52. PWM
Programming the PWM
The PWM
maximum PWM duty cycle for each output to be configured
anywhere from 0% to 100%. This allows the maximum PWM
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)
STEP 6: T
T
control occurs once the programmed T
been exceeded. T
and 100% PWM where the fan speed changes linearly. Otherwise
stated, it is the line drawn between the T
the (T
RANGE
Value (decimal) = PWM
Value (decimal) − 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 80 (hex)
Value (decimal) = 75/0.39 = 192 (decimal)
Value = 192 (decimal) or C0 (hex)
MAX
MIN
is the range of temperature over which automatic fan
PWM
PWM
+ T
Registers
100%
MAX
MAX
RANGE
MIN
0%
RANGE
MAX
registers are 8-bit registers that allow the
Determines Maximum PWM Duty Cycle Below the THERM
RANGE
FOR TEMPERATURE CHANNELS
)/PWM 100% intersection points.
is the temperature range between PWM
T
MIN
Temperature Limit
MAX
MAX
Registers
/0.39
TEMPERATURE
MIN
MIN
temperature has
/PWM
MAX
register is
MIN
and
Rev. B | Page 41 of 68
MIN
The T
1.
2.
3.
4.
As PWM
changes.
Figure 54. Adjusting PWM
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.
Using the ADT7475 evaluation software, graphically
program and visualize this functionality. Ask your local
Analog Devices, Inc. representative for details.
RANGE
PWM
MIN
100%
100%
50%
33%
0%
is determined by the following procedure:
Figure 53. T
MIN
0%
is changed, the automatic fan control slope also
T
RANGE
MIN
T
MIN
MIN
Parameter Affects Cooling Slope
Changes the Automatic Fan Control Slope
30°C
T
RANGE
TEMPERATURE
ADT7475