adt7476a Analog Devices, Inc., adt7476a Datasheet - Page 44

• Manufacturer Part Number: adt7476a
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

ADT7476A
Programming the PWM Maximum Duty Cycle Registers
The PWM maximum duty cycle registers are 8-bit 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%.
The value to be programmed into the PWM maximum 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
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
(T
RANGE
MIN
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)
+ T
is the range of temperature over which automatic fan
PWM
RANGE
100%
MIN
Figure 57. T
0%
RANGE
)/PWM100% intersection points.
RANGE
FOR TEMPERATURE CHANNELS
RANGE
T
is the temperature range between PWM
MIN
Parameter Affects Cooling Slope
MAX
/0.39
T
RANGE
TEMPERATURE
MIN
MIN
/PWM
temperature has
MIN
and the
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MIN
The T
1.
2.
3.
4.
As PWM
As T
the fans reach 100% speed with a smaller temperature change.
Figure 58. 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 ADT7476A evaluation software, you can
graphically program and visualize this functionality.
RANGE
RANGE
100%
MIN
100%
10%
50%
33%
is changed, the slope changes. As T
0%
0%
Figure 59. Increasing T
is determined by the following procedure:
is changed, the automatic fan control slope changes.
T
MIN–HYST
T
T
MIN
MIN
MIN
Changes the Automatic Fan Control Slope.
RANGE
30°C
30°C
40°C
45°C
Changes the AFC slope
54°C
RANGE
gets smaller,