THMC50_08 Datasheet, PDF (19/34 Pages) Texas Instruments – REMOTE/LOCAL TEMPERATURE MONITOR AND FAN CONTROLLER WITH SMBus INTERFACE

THMC50
REMOTE/LOCAL TEMPERATURE MONITOR AND
FAN CONTROLLER WITH SMBus INTERFACE
SLIS090 – JULY 1999
PRINCIPLES OF OPERATION
temperature interrupt operation (continued)
100°C
90°C
80°C
70°C
60°C
50°C
40°C
High
Temp
Low
†
†
†
†
†
†
INT
ACPI control
methods clear
event
ACPI control
methods clear
event
† _{ACPI control methods adjust temperature limit values.}
ACPI control
methods clear
event
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.
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