NCT7491RQR2G【PDF 58/80 页】IC REMOTE THERMAL MONITOR 24QSOP

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NCT7491

http://onsemi.com

Table 74. REGISTER 0x63 Enhanced Acoustics Register 2 (PowerOn Default = 0x00)

Bit

Description

R/W (Note 25)

Name

<6:4>

ACOU2

R/W

These bits define the maximum rate of change of the PWM2 output. Instead of the fan speed

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

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

Time Slot Increase

Time for 0% to 100%

000 = 1

37.5 sec

001 = 2

18.8 sec

010 = 3

12.5 sec

011 = 4

7.5 sec

100 = 8

4.7 sec

101 = 12

3.1 sec

110 = 24

1.6 sec

111 = 48

0.8 sec

<7>

EN2

R/W

When this bit is 1, smoothing is enabled on the PWM2 output.

25.These registers become readonly when the NCT7491 is in automatic fan control mode.

Table 75. PWM MINIMUM DUTY CYCLE REGISTERS

R/W (Note 26)

Description

PowerOn Default

0x64

R/W

PWM1 minimum duty cycle.

0x80 (50% duty cycle)

0x65

R/W

PWM2 minimum duty cycle.

0x80 (50% duty cycle)

0x66

R/W

PWM3 minimum duty cycle.

0x80 (50% duty cycle)

Bit

Name

R/W (Note 26)

Description

<7:0>

PWM duty cycle

R/W

These bits define the PWM

MIN

duty cycle for PWMx.

0x00 = 0% duty cycle (fan off).

0x40 = 25% duty cycle.

0x80 = 50% duty cycle.

0xFF = 100% duty cycle (fan full speed).

26.These registers become readonly when the NCT7491 is in automatic fan control mode.

Table 76. T

MIN

REGISTERS (Note 27)

R/W

Description

PowerOn Default

0x67

R/W

Remote 1 Temperature T

MIN

0x5A (90癈)

0x68

R/W

Local Temperature T

MIN

0x5A (90癈)

0x69

R/W

Remote 2 Temperature T

MIN

0x5A (90癈)

27.These are the T

MIN

registers for each temperature channel. When the temperature measured exceeds T

MIN

, the appropriate fan runs at

minimum speed and increases with temperature according to T

RANGE

Table 77. THERM

LIMIT REGISTERS (Note 28)

R/W

Description

PowerOn Default

0x6A

R/W

Remote 1 THERM

limit.

0x64 (100癈)

0x6B

R/W

Local THERM

limit.

0x64 (100癈)

0x6C

R/W

Remote 2 THERM

limit.

0x64 (100癈)

28.If any temperature measured exceeds its THERM

limit, all PWM outputs drive their fans at 100% duty cycle. This is a failsafe mechanism

incorporated to cool the system in the event of a critical over temperature. It also ensures some level of cooling in the event that software

or hardware locks up. If set to 0x80, this feature is disabled. The PWM output remains at 100% until the temperature drops below THERM

limit hysteresis. If the THERM

pin is programmed as an output, exceeding these limits by 0.25癈 can cause the THERM

pin to assert low

as an output.

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