EVAL-ADT7475EB ON Semiconductor, EVAL-ADT7475EB Datasheet - Page 25

• Manufacturer Part Number: EVAL-ADT7475EB
• Description: BOARD EVALUATION FOR ADT7475
• Manufacturer: ON Semiconductor
• Series: dBCool®r
• Type: Temperature Sensorr

Specifications of EVAL-ADT7475EB

• Contents: Evaluation Board
• For Use With/related Products: ADT7475
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

TACH Pulses per Revolution Register
Bits [1:0] Fan 1 default = 2 pulses per revolution.
Bits [3:2] Fan 2 default = 2 pulses per revolution.
Bits [5:4] Fan 3 default = 2 pulses per revolution.
Bits [7:6] Fan 4 default = 2 pulses per revolution.
Fan Spin−Up
the fan at 100% PWM duty cycle until two TACH pulses are
detected on the TACH input. Once two TACH pulses have
been detected, the PWM duty cycle goes to the expected
running value, for example, 33%. The advantage is that fans
have different spin−up characteristics and take different
times to overcome inertia. The ADT7475 runs the fans just
fast enough to overcome inertia and is quieter on spin−up
than fans programmed to spin up for a given spin−up time.
Fan Startup Timeout
up (because it is below running speed), the ADT7475
includes a fan startup timeout function. During this time, the
ADT7475 looks for two TACH pulses. If two TACH pulses
are not detected, an interrupt is generated. Using
Configuration Register 1 (0x40), Bit 5 (FSPDIS), this
functionality can be changed (see the Disabling Fan Startup
Timeout section).
PWM1, PWM2, PWM3 Configuration Registers
(0x5C, 0x5D, and 0x5E)
Bits [2:0] SPIN, startup timeout for PWM1 = 0x5C,
PWM2 = 0x5D, and PWM3 = 0x5E.
Disabling Fan Startup Timeout
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
duty cycle (non−inverted) or low for 100% duty cycle
(inverted).
The ADT7475 has a unique fan spin−up function. It spins
To prevent the generation of false interrupts as a fan spins
Although fan startup makes fan spin−ups much quieter
The PWM outputs can be programmed high for 100%
00 = 1 pulse per revolution
01 = 2 pulses per revolution
10 = 3 pulses per revolution
11 = 4 pulses per revolution
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
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PWM1 Configuration Register (0x5C)
Bit 4 INV
0 = Logic high for 100% PWM duty cycle.
1 = Logic low for 100% PWM duty cycle.
PWM2 Configuration Register (0x5D)
Bit 4 INV
0 = Logic high for 100% PWM duty cycle.
1 = Logic low for 100% PWM duty cycle.
PWM3 Configuration Register (0x5E)
Bit 4 INV
0 = Logic high for 100% PWM duty cycle.
1 = Logic low for 100% PWM duty cycle.
Low Frequency Mode PWM Drive Frequency
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.
High Frequency Mode PWM Drive
Register 0x61 enables high frequency mode for Fan 1,
Fan 2, and Fan 3, respectively.
PWM Frequency Registers (0x5F to 0x61)
Bits [2:0] FREQ
Fan Speed Control
and manual mode as follows:
•
•
The PWM drive frequency can be adjusted for the
Setting Bit 3 of Register 0x5F, Register 0x60, and
The ADT7475 controls fan speed using automatic mode
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 of this is, if the system hangs, the user is
guaranteed that the system is protected from overheating.
For more information about how 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 ADT7475 allows
the duty cycle of any PWM output to be manually
adjusted. This can be useful if the user wants to change
fan speed at the software level 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.
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