adt7476a Analog Devices, Inc., adt7476a Datasheet - Page 34

• Manufacturer Part Number: adt7476a
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

ADT7476A
PWM3 Configuration (0x5E)
[4] INV.
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
High Frequency Mode PWM Drive
Setting Bit 3 of Register 0x5F, Register 0x60, and Register 0x61
enables high frequency mode for Fan1, 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:
•
•
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
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 Con-
figuration) control the behavior of each PWM output.
0 = Logic high for 100% PWM duty cycle
1 = Logic low for 100% PWM duty cycle
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PWM Configuration Registers (0x5C to 0x5E)
[7:5] BHVR.
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 PWM
Example 1: For a PWM duty cycle of 50%,
Example 2: For a PWM duty cycle of 33%,
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.
PROGRAMMING T
T
For the ADT7467, ADT7468 and ADT7473, T
a slope. For the ADT7475 andADT7476A, T
slope, but defines the temperature region where the PWM
output linearly ramps from PWM
RANGE
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)
PWM = 100%
defines the distance between T
PWM = 0%
PWM
PWM
MIN
MAX
MIN
register is given by
T
MIN
RANGE
Figure 46. T
T
RANGE
MIN
/0.39
MIN
RANGE
to 100% PWM.
MIN
and 100% PWM.
RANGE
RANGE
is no longer a
is effectively