ADT7468 Analog Devices, Inc., ADT7468 Datasheet - Page 34

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

ADT7468
PWM LOGIC STATE
The PWM outputs can be programmed high for 100% duty
cycle (noninverted) or low for 100% duty cycle (inverted).
PWM1 Configuration (Reg. 0x5C)
<4> INV
0 = Logic high for 100% PWM duty cycle
1 = Logic low for 100% PWM duty cycle
PWM2 Configuration (Reg. 0x5D)
<4> INV
0 = Logic high for 100% PWM duty cycle
1 = Logic low for 100% PWM duty cycle
PWM3 Configuration (Reg. 0x5E)
<4> INV
0 = Logic high for 100% PWM duty cycle
1 = Logic low for 100% PWM duty cycle
Low Frequency Mode PWM Drive Frequency
The PWM drive frequency can be adjusted for the application.
Register 0x5F to Register 0x61 configure the PWM frequency
for PWM1 to PWM3, respectively. In high frequency mode,
the PWM drive frequency is always 22.5 kHz and cannot
be changed.
PWM1 Frequency Registers (Reg. 0x5F to Reg. 0x61)
<2:0> frequency
FAN SPEED CONTROL
The ADT7468 controls fan speed using two modes: automatic
and manual.
In automatic fan speed control mode, fan speed automatically
varies with temperature, without CPU intervention, once initial
parameters are set up. The advantage is that, if the CPU hangs,
the user is guaranteed that the system is protected from
000 = 11.0 Hz
001 = 14.7 Hz
010 = 22.1 Hz
011 = 29.4 Hz
100 = 35.3 Hz default
101 = 44.1 Hz
110 = 58.8 Hz
111 = 88.2 Hz
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overheating. The automatic fan speed control incorporates a
feature called dynamic T
design effort required to program the automatic fan speed
control loop. See the Programming the Automatic Fan Speed
Control Loop section.
In manual fan speed control mode, the ADT7468 allows the
duty cycle of any PWM output to be manually adjusted. This
can be useful if the user wants to change fan speed in the
software or adjust PWM duty cycle output for test purposes.
Bits <7:5> of Reg. 0x5C to Reg. 0x5E (PWM Configuration)
control the behavior of each PWM output.
PWM Configuration Register (Reg. 0x5C to Reg. 0x5E)
<7:5> BHVR
Once under manual control, each PWM output can be
manually updated by writing to Reg. 0x30 to Reg. 0x32 (PWMx
current duty cycle registers).
Programming the PWM Current Duty Cycle Registers
The PWM current duty cycle registers are 8-bit registers that
allow the PWM duty cycle for each output to be set anywhere
from 0% to 100% in steps of 0.39%. The value to be program-
med into the PWM
Example 1: For a PWM duty cycle of 50%,
Example 2: For a PWM duty cycle of 33%,
PWM Duty Cycle Registers
Reg. 0x30 PWM1 duty cycle = 0x00 (0% default)
Reg. 0x31 PWM2 duty cycle = 0x00 (0% default)
Reg. 0x32 PWM3 duty cycle = 0x00 (0% default)
By reading the PWMx current duty cycle registers, the user can
keep track of the current duty cycle on each PWM output, even
when the fans are running in automatic fan speed control mode
or acoustic enhancement mode. See the Programming the
Automatic Fan Speed Control Loop section for details.
111 = manual mode
Value (decimal) = PWM
Value (decimal) = 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 0x80 (hex)
Value (decimal) = 33/0.39 = 85 (decimal)
Value = 85 (decimal) or 0x54 (hex)
MIN
register is given by
MIN
calibration, which reduces the
MIN
/0.39