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Table 35. Register 0x3C — PECI TRANGE/Enhanced Acoustics Register (Power−On Default = 0xC0)

Bit No.

Mnemonic

R/W (Note 1)

Description

[2:0]

ACOU

R/W

Assuming that PWMx is associated with the PECI channel, these bits define the maximum

rate of change of the PWMx output for PECI temperature−related changes. Instead of the fan

speed jumping instantaneously to its newly determined speed, it ramps gracefully at the rate

determined by these bits. This feature ultimately enhances the acoustics of the fan. The

smoothing times below are based on a refresh rate of the round robin cycle. The PECI data,

for 0% to 100%, must be multiplied each time by:

PECI Refresh Rate

Round Robin Cycle

where the PECI refresh rate is defined in Register 0x36 and the round robin cycle is typically

165 ms.

When Bit 7 of Configuration Register 6 (0x10) is 0

Bit Code

Time for 0% to 100%

000 = 1

001 = 2

010 = 3

011 = 4

100 = 8

101 = 12

110 = 24

111 = 48

37.5 sec

18.8 sec

12.5 sec

7.5 sec

4.7 sec

3.1 sec

1.6 sec

0.8 sec

[2:0]

ACOU

R/W

When Bit 7 of Configuration Register 6 (0x10) is 1

Bit Code

Time for 0% to 100%

000 = 1

001 = 2

010 = 3

011 = 4

100 = 8

101 = 12

110 = 24

111 = 48

52.2 sec

26.1 sec

17.4 sec

10.4 sec

6.5 sec

4.4 sec

2.2 sec

1.1 sec

[3]

ENP

R/W

When this bit is set to 1, smoothing is enabled on the PECI channel allowing enhanced

acoustics on the associated PWM output.

[7:4]

RANGE

R/W

These bits determine the PWM duty cycle vs. the temperature range for automatic fan

control.

Bit Code

Temperature

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

1011

1100

1101

1110

1111

2°C

2.5°C

3.33°C

4°C

5°C

6.67°C

8°C

10°C

13.33°C

16°C

20°C

26.67°C

32°C (default)

40°C

53.33°C

80°C

1. This register becomes read-only when the Configuration Register 1 (0x40) LOCK bit is set to 1. Any subsequent attempts to write to this

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