ADT7468 Analog Devices, Inc., ADT7468 Datasheet - Page 47

• Manufacturer Part Number: ADT7468
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

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
by
Example 1: For a maximum PWM duty cycle of 50%,
Example 2: For a minimum PWM duty cycle of 75%,
PWM
Reg. 0x38, PWM1 Maximum Duty Cycle = 0xFF (100% default)
Reg. 0x39, PWM2 Maximum Duty Cycle = 0xFF (100% default)
Reg. 0x3A, PWM3 Maximum Duty Cycle = 0xFF
(100% default)
See the Note on Fan Speed and PWM Duty Cycle.
STEP 6: T
T
control occurs once the programmed T
been exceeded. T
value; that is, a T
33%. If PWM
changes.
RANGE
Figure 61. 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
is the range of temperature over which automatic fan
PWM
PWM
100%
Registers
MAX
MAX
RANGE
MIN
0%
MIN
registers are 8-bit registers that allow the
MAX
RANGE
is increased or decreased, the effective T
RANGE
for Temperature Channels
Determines Maximum PWM Duty Cycle Below the
THERM Temperature Limit
of 40°C holds true only for PWM
T
is a temperature slope, not an arbitrary
MIN
MAX
MAX
Registers
/0.39
TEMPERATURE
MIN
temperature has
MAX
register is given
MIN
RANGE
=
Rev. A | Page 47 of 84
The T
procedure:
1.
2.
3.
4.
T
is changed, T
same. The higher the PWM
T
temperature.
RANGE
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.
Using the ADT7468 evaluation software, you can
graphically program and visualize this functionality. Ask
your local Analog Devices representative for details.
RANGE
, that is, the fan reaches full speed (100%) at a lower
is implemented as a slope, which means that as PWM
PWM
100%
50%
33%
100%
0%
or fan control slope is determined by the following
MIN
0%
Figure 62. T
RANGE
Figure 63. Adjusting PWM
changes, but the actual slope remains the
T
RANGE
MIN
T
MIN
Parameter Affects Cooling Slope
MIN
value, the smaller the effective
30°C
40°C
T
RANGE
MIN
TEMPERATURE
Affects T
RANGE
ADT7468
MIN