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ADM1024

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Once the interrupt has been cleared, it will not be

reasserted even if the temperature remains above the high

limit(s). However, INT will be reasserted if:

The temperature falls below the low limit for the sensor;

or:

The high limit(s) is/are reprogrammed to a new value, and

the temperature then rises above the new high limit on the

next monitoring cycle;

or:

The THERM pin is pulled low externally, which sets Bit 5

of Interrupt Status Register 2;

or:

An interrupt is generated by another source.

Similarly, should the temperature measured by a sensor

start off within limits then fall below the low limit, INT will

be asserted. Once cleared, it will not be reasserted unless:

The temperature rises above the high limit;

or:

The low limit(s) is/are reprogrammed, and the temperature

then falls below the new low limit;

or:

The THERM pin is pulled low externally, which sets Bit 5

of Interrupt Status Register 2;

or:

An interrupt is generated by another source.

THERM Input/Output

The Thermal Management Input/Output (THERM) is a

logic input/output with an internal, 100 k

W pullup resistor,

that provides a separate output for temperature interrupts

only. It is enabled by setting Bit 2 of Configuration Register 1.

The THERM output has two operating modes that can be

programmed by Bit 3 of Configuration Register 2 (address

4Ah). With this bit set to the default value of 0, the THERM

output operates in “Default” interrupt mode. With this bit set

to 1, the THERM output operates in “ACPI” mode.

Thermal interrupts can still be generated at the INT output

while THERM is enabled, but if these are not required they can

be masked by writing a 1 to Bit 0 of Configuration Register 2

(address 4Ah). The THERM pin can also function as a logic

input for an external sensor, for example, a temperature sensor

such as the ADM22105 used in Figure 35. If THERM is taken

low by an external source, the analog output will be forced to

FFh to switch a controlled fan to maximum speed. This also

generates an INT output as previously described.

Default Mode

In Default mode, the THERM output operates like a

thermostat with hysteresis. THERM will go low and Bit 5 of

Interrupt Status Register 2 will be set, if the temperature

measured by any of the sensors exceeds the high limit

programmed for that sensor. It will remain asserted until

reset by reading Interrupt Status Register 2, by setting Bit 6

of Configuration Register 1, or when the temperature falls

below the low limit programmed for that sensor.

Figure 34. INT or THERM Output in Default Mode

TEMP

HIGH LIMIT

TEMP

LOW LIMIT

THERM

CLEARED BY

READ OR

THERM CLEAR

PROGRAMMED

VALUE

ANALOG

OUTPUT

CLEARED BY

TEMP FALLING

BELOW LOW

LIMIT

0xFF

EXT

THERM

INPUT

If THERM is cleared by reading the status register, it will

be reasserted after the next temperature reading and

comparison if it remains above the high limit.

If THERM is cleared by setting Bit 6 of Configuration

THERM will also be asserted if one of the hardware

temperature limits at addresses 13h, 14h, 17h, or 18h is

exceeded for three consecutive measurements. When this

happens, the analog output will be forced to FFh to boost a

controlled cooling fan to full speed.

Reading Status Register 1 will not clear THERM in this

case, because errors caused by exceeding the hardware

temperature limits are stored in a separate register that is not

cleared by reading the status register. In this case, THERM

can only be cleared by setting Bit 0 of Configuration

THERM will be cleared automatically if the temperature

falls at least 5 degrees below the limit for three consecutive

measurements.

ACPI Mode

In ACPI mode, THERM responds only to the hardware

temperature limits at addresses 13h, 14h, 17h, and 18h, not

to the software−programmed limits.

Figure 35. THERM Output in ACPI Mode

TEMP

HARDWARE

TRIP POINT

THERM

ANALOG

OUTPUT

PROGRAMMED

VALUE

0xFF

THERM

EXT

INPUT

THERM will go low if either the internal or external

hardware temperature limit is exceeded for three

consecutive measurements. It will remain low until the

temperature falls at least 5 degrees below the limit for three

consecutive measurements. While THERM is low, the

analog output will go to FFh to boost a controlled fan to full

speed.

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