ADT7476ARQH ONSEMI [ON Semiconductor], ADT7476ARQH Datasheet - Page 40

• Manufacturer Part Number: ADT7476ARQH
• Description: dBCOOL Remote Thermal Controller and Voltage Monitor
• Manufacturer: ONSEMI [ON Semiconductor]

Programming the PWM Maximum Duty Cycle
Registers
registers that allow the 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%.
duty cycle register is given by:
Example 1: For a maximum PWM duty cycle of 50%,
Example 2: For a minimum PWM duty cycle of 75%,
PWM Maximum Duty Cycle Registers
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
fan control occurs once the programmed T
has been exceeded. T
PWM
linearly. Otherwise stated, it is the line drawn between the
T
intersection points.
The T
MIN
Figure 57. T
The PWM maximum duty cycle registers are 8−bit
The value to be programmed into the PWM maximum
T
RANGE
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)
1. Determine the maximum operating temperature for
2. Determine experimentally the fan speed (PWM
/PWM
MIN
RANGE
that channel (for example, 70°C).
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.
PWM
RANGE
100%
and 100% PWM where the fan speed changes
is the range of temperature over which automatic
MIN
MIN
0%
is determined by the following procedure:
RANGE
and the (T
for Temperature Channels
T
RANGE
MIN
Parameter Affects Cooling Slope
is the temperature range between
MAX
MIN
/0.39
T
+ T
RANGE
TEMPERATURE
RANGE
MIN
)/PWM100%
temperature
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40
changes.
gets smaller, the fans reach 100% speed with a smaller
temperature change.
Figure 58. Adjusting PWM
Figure 60. Changing PWM Max Does Not Change the
As PWM
As T
3. Determine the slope of the required control loop to
4. Using the ADT7476 evaluation software, you can
Figure 59. Increasing T
meet these requirements.
graphically program and visualize this
functionality.
RANGE
100%
100%
100%
PWM
MAX
10%
50%
33%
10%
T
0%
0%
0%
MIN–HYST
MIN
T
MIN–HYST
is changed, the slope changes. As T
is changed, the automatic fan control slope
T
T
MIN
MIN
Fan Control Slope
AFC Slope
AFC Slope
MIN
T
30°C
RANGE
30°C
40°C
RANGE
Changes the Automatic
45°C
54°C
Changes the
RANGE