Table of Contents
Advertisement
100%
PWM
MAX
PWM
MIN
0%
T
MIN
Figure 52. PWM
Determines Maximum PWM Duty Cycle
MAX
Below the THERM Temperature Limit
Programming the PWM
MAX
The PWM
registers are 8-bit registers that allow the
MAX
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
Value (decimal) = PWM
Example 1: For a maximum PWM duty cycle of 50%,
Value (decimal) – 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 80 (hex)
Example 2: For a minimum PWM duty cycle of 75%,
Value (decimal) = 75/0.39 = 85 (decimal)
Value = 192 (decimal) or C0 (hex)
PWM
Registers
MAX
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.
TEMPERATURE
Registers
register is
MAX
/0.39
MAX
STEP 6: T
RANGE
T
is the range of temperature over which automatic fan
RANGE
control occurs once the programmed T
exceeded. T
RANGE
that is, a T
RANGE
PWM
is increased or decreased, the effective T
MIN
Refer to Figure 53.
100%
PWM
MIN
0%
Figure 53. T
The T
or fan control slope is determined by the following
RANGE
procedure:
1.
Determine the maximum operating temperature for that
channel (for example, 70°C).
2.
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).
3.
Determine the slope of the required control loop to meet
these requirements.
4.
Can graphically program and visualize this functionality
using the ADT7473 evaluation software. Ask your local
Analog Devices representative for details.
Figure 54 shows how adjusting PWM
100%
50%
33%
0%
Figure 54. Adjusting PWM
Rev. 0 | Page 39 of 76
FOR TEMPERATURE CHANNELS
temperature is
MIN
is a temperature slope, not an arbitrary value,
of 40°C holds true only for PWM
T
RANGE
T
TEMPERATURE
MIN
Parameter Affects Cooling Slope
RANGE
affects T
MIN
30°C
40°C
T
MIN
Affects T
MIN
ADT7473
= 33%. If
MIN
changes.
RANGE
.
RANGE
RANGE
Advertisement
Table of Contents
