THMC50

REMOTE/LOCAL TEMPERATURE MONITOR AND

FAN CONTROLLER WITH SMBus INTERFACE

SLIS090 – JULY 1999

19

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

temperature interrupt operation (continued)

100

°C

High

Low

Temp

ACPI control

methods clear

event

ACPI control

methods clear

event

ACPI control

methods clear

event

†

†

†

†

†

†

90

°C

80

°C

70

°C

60

°C

50

°C

40

°C

† ACPI control methods adjust temperature limit values.

INT

Figure 15. Examples of Temperature Interrupt Events

THERM operation

The THERM output is used for fault tolerant fan control. It is asserted by the THMC50 whenever the remote

thermal diode temperature or ambient temperature exceeds the appropriate automatic trip point for three

consecutive acquisitions (see Figure 16). The remote and local thermal diode trip point values are contained

in the programmable remote/local temperature automatic trip point registers (if bit 3 in the configuration register

is set) or the default remote/local temperature automatic trip point (if bit 3 in the configuration register is cleared).

The default trip points are hardware-set trip points that can be read from the value RAM. Programmable trip

points provide for increased flexibility in the ability to tailor the thermal characteristics of the system. The

programmable values can be written to, and then locked down, by writing a 1 to the

write once bit located in the

configuration register.

THERM is asserted after three consecutive acquisitions of a remote or an internal temperature that exceeds

the appropriate automatic trip points (based upon bit 3 of the configuration register). When THERM is asserted

by the THMC50, it remains active (with FAN_SPD = 0xFF and FAN_OFF = FLOATING) until both the local and

remote temperatures fall 5

°C below the appropriate automatic trip point values (based upon bit 3 of the

configuration register) for three consecutive temperature acquisitions. Once THERM has been cleared, the

FAN_SPD output returns to its previously programmed value and FAN_OFF returns to its previously

programmed state. Note that when FAN_SPD goes to full scale (0xFF) during a THERM event, the value in the

analog output register (0x19) reflects the previously programmed value and not 0xFF, unless 0xFF was the

previously programmed value. When THERM is asserted internally, it causes INT to be unconditionally

asserted.

An external device that pulls THERM low causes the fan control to be turned to full on and corresponding status

bits to be set. In addition, whenever THERM is active, the FAN_OFF bit in the configuration register is

unconditionally set. Note that an INT generated by an external device pulling THERM low is maskable, but an

INT generated by an internally generated THERM condition is not maskable.