ADT7476ARQZ-R7 datasheet(45/67 Pages) ONSEMI

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ADT7476

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Enhance Acoustics Register 1 (0x62)

Bit 7 (MIN3) = 0, PWM3 is off (0% PWM duty cycle) when

temperature is below TMIN − THYST.

Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty cycle

below TMIN − THYST.

Bit 6 (MIN2) = 0, PWM2 is off (0% PWM duty cycle) when

temperature is below TMIN − THYST.

Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty cycle

below TMIN − THYST.

Bit 5 (MIN1) = 0, PWM1 is off (0% PWM duty cycle) when

temperature is below TMIN − THYST.

Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty cycle

below TMIN − THYST.

Configuration Register 6 (0x10)

[0] SLOW = 1, slows the ramp rate for PWM changes

associated with the Remote 1 temperature channel by a factor

of 4.

[1] SLOW = 1, slows the ramp rate for PWM changes

associated with the local temperature channel by a factor of 4.

[2] SLOW = 1, slows the ramp rate for PWM changes

associated with the Remote 2 temperature channel by a factor

of 4.

[7] ExtraSlow = 1, slows the ramp rate for all fans by a factor

of 39.2%.

The following sections list the ramp−up times when

enhanced acoustics is enabled for each temperature channel.

Enhance Acoustics Register 1 (0x62)

[2:0] ACOU selects the ramp rate for PWM outputs

associated with the Remote Temperature 1 input.

000 = 37.5 sec

001 = 18.8 sec

010 = 12.5 sec

011 = 7.5 sec

100 = 4.7 sec

101 = 3.1 sec

110 = 1.6 sec

111 = 0.8 sec

Enhance Acoustics Register 2 (0x63)

[2:0] ACOU3 selects the ramp rate for PWM outputs

associated with the local temperature channel.

000 = 37.5 sec

001 = 18.8 sec

010 = 12.5 sec

011 = 7.5 sec

100 = 4.7 sec

101 = 3.1 sec

110 = 1.6 sec

111 = 0.8 sec

[6:4] ACOU2 selects the ramp rate for PWM outputs

associated with the Remote Temperature 2 input.

000 = 37.5 sec

001 = 18.8 sec

010 = 12.5 sec

011 = 7.5 sec

100 = 4.7 sec

101 = 3.1 sec

110 = 1.6 sec

111 = 0.8 sec

When Bit 7 of Configuration Register 6 (0x10) = 1, the

above ramp rates change to the values below.

000 = 52.2 sec

001 = 26.1 sec

010 = 17.4 sec

011 = 10.4 sec

100 = 6.5 sec

101 = 4.4 sec

110 = 2.2 sec

111 = 1.1 sec

Setting the appropriate slow bit [2:0] of Configuration

Fan Presence Detect

This feature is used to determine if a 4−wire fan is directly

connected to a PWM output. This feature does not work for

3−wire fans. To detect whether a 4−wire fan is connected

directly to a PWM output, the following must be performed

in this order:

1. Drive the appropriate PWM outputs to 100%

duty cycle.

2. Set Bit 0 of Configuration Register 2 (0x73).

3. Wait 5 ms.

4. Program fans to run at a different speed if necessary.

5. Read the state of Bits [3:1] of Configuration

whether a 4−wire fan is directly connected to the

PWM output.

As the detection time only takes 5 ms, programming the

PWM outputs to 100% and then back to its normal speed is

not noticeable in most cases.

How Fan Presence Detect Works

4−wire fans typically have an internal pull up to 4.75 V

±10%, which typically sources 5 mA. While the detection

cycle is on, an internal current sink is turned on, which sinks

current from the fan’s internal pullup. By driving some of the

current from the fan’s internal pullup (~100

mA) the logic

buffer switches to a defined logic state. If this state is high,

a fan is present; if the state is low, no fan is present.

Note: The PWM input voltage should be clamped to 3.3 V.

This ensures the PWM output is not pulled to a voltage

higher than the maximum allowable voltage on that pin

(5.5 V).

ADT7476ARQZ-R7 Datasheet(PDF) 45 Page - ON Semiconductor

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