ADT7476ARQZ-R7 datasheet(59/67 Pages) ONSEMI

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ADT7476

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Table 34. PWM Minimum Duty Cycle Registers

R/W (Note 1)

Description

Power−On 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 No.

Name

R/W

Description

[7:0]

PWM duty

cycle

R/W

These bits define the PWMMIN 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).

1. These registers become read−only when the ADT7476 is in automatic fan control mode.

Table 35. TMIN Registers (Note 1)

R/W (Note 2)

Description

Power−On Default

0x67

R/W

Remote 1 temperature TMIN.

0x5A (90°C)

0x68

R/W

Local temperature TMIN.

0x5A (90°C)

0x69

R/W

Remote 2 temperature TMIN.

0x5A (90°C)

1. These are the TMIN registers for each temperature channel. When the temperature measured exceeds TMIN, the appropriate fan runs at

minimum speed and increases with temperature according to TRANGE.

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

Table 36. THERM Limit Registers (Note 1)

R/W (Note 2)

Description

Power−On Default

0x6A

R/W

Remote 1 THERM temperature limit.

0x64 (100°C)

0x6B

R/W

Local THERM temperature limit.

0x64 (100°C)

0x6C

R/W

Remote 2 THERM temperature limit.

0x64 (100°C)

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 37. Temperature/TMIN Hysteresis Registers (Note 1)

R/W (Note 2)

Description

Power−On Default

0x6D

R/W

Remote 1 and local temperature hysteresis.

0x44

[3:0]

HYSL

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

applied to the local temperature AFC control loops.

[7:4]

HYSR1

Remote 1 temperature hysteresis. 0°C to 15°C of hysteresis can

be applied to the Remote 1 temperature AFC control loops.

0x6E

R/W

Remote 2 temperature hysteresis.

0x40

0x6E

HYSR2

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

applied to the local temperature AFC control loops.

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 TMIN value, the fan remains running at PWMMIN duty cycle until the temperature = TMIN – hysteresis. Up to 15°C of

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 TMIN.

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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