REV. C

ADT7463

–45–

Table XXIII. PWM Min Duty Cycle Registers

Register Address

R/W*

Description

Power-On Default

0x64

Read/Write

PWM1 Min Duty Cycle

0x80 (50% duty cycle)

0x65

Read/Write

PWM2 Min Duty Cycle

0x80 (50% duty cycle)

0x66

Read/Write

PWM3 Min Duty Cycle

0x80 (50% duty cycle)

Bit

Name

Read/Write

Description

<7:0>

PWM Duty

Read/Write

Cycle

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

0x40 = 25% duty cycle.

0x80 = 50% duty cycle.

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

*These registers become read-only when the ADT7463 is in automatic fan control mode.

Register Address

R/W*

Description

Power-On Default

0x67

Read/Write

0x5A (90�C)

0x68

Read/Write

0x5A (90�C)

0x69

Read/Write

0x5A (90�C)

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

Table XXV. THERM Limit Registers

Register Address

R/W*

Description

Power-On Default

0x6A

Read/Write

Remote 1 THERM Limit

0x64 (100�C)

0x6B

Read/Write

Local THERM Limit

0x64 (100�C)

0x6C

Read/Write

Remote 2 THERM Limit

0x64 (100�C)

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, then

exceeding these limits by 0.25�C can cause the THERM pin to assert low as an output.

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

Table XXVI. Temperature Hysteresis Registers

Register Address

R/W*

Description

Power-On Default

0x6D

Read/Write

Remote 1 Local Temp Hysteresis

0x44

0x6E

Read/Write

Remote 2 Temp Hysteresis

0x40

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

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

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

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