ADT7476ARQZ-R7 datasheet(30/67 Pages) ONSEMI

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ADT7476

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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

Instead, the fan spins up for the fixed time as selected in

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 ADT7476 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 ADT7476

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

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.

ADT7476ARQZ-R7 Datasheet(PDF) 30 Page - ON Semiconductor

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