ON Semiconductor ADT7476AARQZ-R Manual page 61

Remote thermal controller and voltage monitor

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Table 69. PWM MINIMUM DUTY CYCLE REGISTERS

0x64

0x65

0x66

Bit No.

Name

[7:0]

PWM Duty

Cycle

1. These registers become read-only when the ADT7476A is in automatic fan control mode.

Table 70. T

MIN

0x67

0x68

0x69

1. These are the T

minimum speed and increases with temperature according to T

2. These registers become read-only when the Configuration Register 1 Lock bit is set. Any further attempts to write to these registers have no

effect.

Table 71. THERM LIMIT REGISTERS

0x6A

0x6B

0x6C

1. If any temperature measured exceeds its THERM limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail-safe mechanism

incorporated to cool the system in the event of a critical overtemperature. 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°C can cause the THERM pin to

assert low as an output.

2. These registers become read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to these registers have

no effect.

Table 72. TEMPERATURE/T

0x6D

[3:0]

[7:4]

0x6E

1. Each 4-bit value controls the amount of temperature hysteresis applied to a particular temperature channel. Once the temperature for that

channel falls below its T

hysteresis can be assigned to any temperature channel. The hysteresis value chosen also applies to that temperature channel if its THERM

limit is exceeded. The PWM output being controlled goes to 100% if the THERM limit is exceeded and remains at 100% until the temperature

drops below THERM – hysteresis. For acoustic reasons, it is recommended that the hysteresis value not be programmed less than 4°C.

Setting the hysteresis value lower than 4°C causes the fan to switch on and off regularly when the temperature is close to T

2. These registers become read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to these registers have

no effect.

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R/W

PWM1 Minimum Duty Cycle

R/W

PWM2 Minimum Duty Cycle

R/W

PWM3 Minimum Duty Cycle

R/W

These bits define the PWM

0x00 = 0% Duty Cycle (Fan Off)

0x40 = 25% Duty Cycle

0x80 = 50% Duty Cycle

0xFF = 100% Duty Cycle (Fan Full Speed)

REGISTERS

(Note 1 and 2)

R/W

Remote 1 Temperature T

R/W

Local Temperature T

R/W

Remote 2 Temperature T

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

MIN

(Note 1 and 2)

R/W

Remote 1 THERM Temperature Limit

R/W

Local THERM Temperature Limit

R/W

Remote 2 THERM Temperature Limit

HYSTERESIS REGISTERS

MIN

R/W

Remote 1 and local temperature hysteresis.

HYSL

Local temperature hysteresis. 0°C to 15°C of hysteresis

can be applied to the local temperature AFC control

loops.

HYSR1

Remote 1 temperature hysteresis. 0°C to 15°C of hyster-

esis can be applied to the Remote 1 temperature AFC

control loops.

R/W

Remote 2 temperature hysteresis.

HYSR2

Local temperature hysteresis. 0°C to 15°C of hysteresis

can be applied to the local temperature AFC control

loops.

value, the fan remains running at PWM

MIN

ADT7476A

(Note 1)

Description

duty cycle for PWMx.

MIN

Description

MIN

RANGE

Description

(Note 1 and 2)

Description

duty cycle until the temperature = T

MIN

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Power-On Default

0x80 (50% Duty Cycle)

Power-On Default

0x5A (90°C)

, the appropriate fan runs at

MIN

Power-On Default

0x64 (100°C)

Power-On Default

0x44

0x40

– hysteresis. Up to 15°C of

MIN

ON Semiconductor ADT7476AARQZ-R Manual page 61

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