Analog Devices dBCool ADT7473 Manual page 30

ADT7473
Disabling Fan Startup Timeout
Although fan start-up 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
(0x40) disables the spin-up for two TACH pulses. Instea
fan spins up for the fixed time a
Register 0x5E.
PWM Logic State
The PWM outputs can be programmed high for a 100% duty
cycle (noninverted) or low for a 100% duty cycle (inverted).
PWM1 Configuration Register (0x5C)
Bit 4 INV.
0 = ogic high for a 100% PWM duty cycle L
1 = ogic low for a 100% P L WM duty cycle
PWM2 Configuration Register (0x5D)
Bit 4 INV.
0 = L ogic high for a 100% PWM duty cycle
1 = L ogic low for a 100% PWM duty cycle
PWM3 Configuration Register (0x5E)
Bit 4 INV.
0 = Logic high for a 100% PWM duty cycle
1 = Logic low for a 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, th
PWM drive frequency is always 22.5 kHz.
High Frequency Mode PWM Drive
Setting Bit 3 of Register 0x5F enables high frequency mode
all fans.
PWM Frequency Registers (Register 0x5F to Register
0x61)
Bits [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
d, the
s selected in Register 0x5C to
for
Fan Speed Control
The ADT7473 contro
modes.
1
In automatic fan speed control mode, fan speed is automatically
var d with temperature and without CPU interven ie
ini l parameters are set up. The advantag tia
sys m hangs, the user is guaranteed the sy te
fro overheating. The automatic fan speed control incorp m
a f ture called dynamic T ea
the d esign effort required to program the automatic f
con rol loop. For more information and procedures on how to t
prog ram the automatic fan speed control loo
T calibration, see the Programming the Automatic Fan Speed
MIN
Co trol Loop section. n
In manual fan speed control mode, the ADT7473 allows the
duty cycle of any PWM output to be manually adjusted. Thi
can be useful if the user wants to change fan speed in softwa
or adjust th e PWM duty cycle output for test purposes. Bits
[7:5] of Register 0x5C to Register 0x5E (PWM co
registers) control the behavior
PWM Configuration Registers (Register 0x5C to
Register 0x5E)
Bits [7:5] BHVR
111 = manual mode
Once under manual control, each PWM output can be ma
ally updated by writing to Register 0x30 to Register 0x
current duty cycle registers).
e
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
Value (decimal) = PWM
Example 1: For a PWM duty cycle of 50%
Value (decimal) = 50/0.39 = 128 (decimal)
Value = 128 (decimal) o
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
Register 0x30, PWM1 Duty Cycle = 0x00 (0% default)
Register 0x31, PWM2 Duty Cycle = 0x00 (0% default)
Register 0x32, PWM3 Duty Cycle = 0x00 (0% default)
Rev. A | Page 30 of 76
ls fan speed using automatic and manual
e of this is that, if the
stem is protected
calibration. This feature red
MIN
p and dynamic
nfiguration
of each PWM output.
register is given by
MIN
/0.39
MIN
r 0x80 (hex)
Cycle Registers
tion, once
orates
uces
an speed
s
re
nu-
32 (PWM