ADT7476AARQZ 查看數據表（PDF） - ON Semiconductor
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ADT7476AARQZ Datasheet PDF : 67 Pages
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ADT7476A
PWM1, PWM2, PWM3 Configuration (0x5C, 0x5D,
0x5E)
[2:0] SPIN, startup timeout for PWM1 = 0x5C,
PWM2 = 0x5D, and PWM3 = 0x5E.
000 = No startup timeout
001 = 100 ms
010 = 250 ms default
011 = 400 ms
100 = 667 ms
101 = 1 sec
110 = 2 sec
111 = 4 sec
Disabling Fan Startup Timeout
Although fan startup makes fan spin-ups much quieter
than fixed-time spin-ups, the option exists to use fixed
spin-up times. Setting Bit 5 (FSPDIS) to 1 in Configuration
Register 1 (0x40) disables the spin-up for two TACH pulses.
Instead, the fan spins up for the fixed time as selected in
Register 0x5C to Register 0x5E.
PWM Logic State
The PWM outputs can be programmed high for 100%
duty cycle (noninverted) or low for 100% duty cycle
(inverted).
PWM1 Configuration (0x5C)
[4] INV.
0 = Logic high for 100% PWM duty cycle
1 = Logic low for 100% PWM duty cycle
PWM2 Configuration (0x5D)
[4] INV.
0 = Logic high for 100% PWM duty cycle
1 = Logic low for 100% PWM duty cycle
PWM3 Configuration (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.
PWM1, PWM 2, PWM3 Frequency Registers
(0x5F to 0x61)
[2:0] FREQ
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
High Frequency Mode PWM Drive
Setting Bit 3 of Register 0x5F, Register 0x60, and Register
0x61 enables high frequency mode for Fan 1, Fan 2, and
Fan 3 respectively.
In high frequency mode, the PWM drive frequency is
always 22.5 kHz. When high frequency mode is enabled, the
dc bits are automatically asserted internally and do not need
to be changed.
Fan Speed Control
The ADT7476A controls fan speed using automatic and
manual modes:
• In automatic fan speed control mode, fan speed is
automatically varied with temperature and without CPU
intervention once initial parameters are set up. The
advantage is that if the system hangs, the user is
guaranteed that the system is protected from
overheating.
• In manual fan speed control mode, the ADT7476A
allows the duty cycle of any PWM output to be
adjusted manually. This can be useful if the user wants
to change fan speed in software or adjust PWM duty
cycle output for test purposes. Bits [7:5] of Register
0x5C to Register 0x5E (PWM Configuration) control
the behavior of each PWM output.
PWM Configuration Registers (0x5C to 0x5E)
[7:5] BHVR.
111 = manual mode
Once under manual control, each PWM output can be
manually updated by writing to Register 0x30 to Register
0x32 (PWM 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 programmed into the PWMMIN register is given by:
Value (decimal) = PWMMIN/0.39
Example 1: For a PWM duty cycle of 50%,
Value (decimal) = 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 0x80 (hex)
Example 2: For a PWM duty cycle of 33%,
Value (decimal) = 33/0.39 = 85 (decimal)
Value = 85 (decimal) or 0x54 (hex)
PWM Current Duty Cycle Registers
Register 0x30 PWM1 Current Duty Cycle = 0xFF (100% default)
Register 0x31 PWM2 Current Duty Cycle = 0xFF (100% default)
Register 0x32 PWM3 Current Duty Cycle = 0xFF (100% 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.
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