ADT7490ARQZ-REEL View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADT7490ARQZ-REEL Datasheet PDF : 76 Pages
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ADT7490
Programming the PWMMAX Registers
The PWMMAX 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 PWMMAX register is
given by
Value (decimal) = PWMMAX/0.39
Example 1
For a maximum PWM duty cycle of 50%,
Value (decimal) – 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 0x80 (hex)
Example 2
For a minimum PWM duty cycle of 75%,
Value (decimal) = 75/0.39 = 85 (decimal)
Value = 192 (decimal) or 0xC0 (hex)
PWMMAX Registers
Register 0x38, Maximum PWM1 Duty Cycle = 0xFF
(100% default)
Register 0x39, Maximum PWM2 Duty Cycle = 0xFF
(100% default)
Register 0x3A, Maximum PWM3 Duty Cycle = 0xFF
(100% default)
STEP 6: TRANGE FOR TEMPERATURE CHANNELS
TRANGE is the range of temperature over which automatic fan
control occurs once the programmed TMIN temperature has
been exceeded. TRANGE is the temperature range between PWMMIN
and 100% PWM where the fan speed changes linearly. Otherwise
stated, it is the line drawn between the TMIN/PWMMIN and the
(TMIN + TRANGE)/100% PWM intersection points.
TRANGE
100%
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. Using the ADT7490 evaluation software, graphically
program and visualize this functionality. Ask a local
Analog Devices representative for details.
As PWMMIN is changed, the automatic fan control slope changes.
100%
50%
33%
0%
30°C
TMIN
Figure 55. Adjusting PWMMIN Changes the Automatic Fan Control Slope
As TRANGE is changed, the slope changes. As TRANGE gets smaller,
the fans reach 100% speed with a smaller temperature change.
100%
10%
0%
TMIN–HYST
30°C
40°C
45°C
54°C
TMIN
Figure 56. Increasing TRANGE Changes the AFC slope
PWMMIN
0%
TMIN
TEMPERATURE
Figure 54. TRANGE Parameter Affects Cooling Slope
The TRANGE is determined by the following 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-
100%
MAX
PWM
10%
0%
TMIN–HYST
TRANGE
Figure 57. Changing PWM Max Does Not Change the AFC Slope
Rev. 0 | Page 41 of 76
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