ADT7482ARMZ-REEL View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

ADT7482ARMZ-REEL

Dual Channel Temperature Sensor and Overtemperature Alarm

Analog Devices 

ADT7482

low temperature limits, the ALERT output is asserted low. An

open-circuit fault on the remote diode also causes ALERT to

assert. ALERT is reset when serviced by a master reading its

device address, provided the error condition has gone away, and

the status register has been reset.

The THERM output asserts low if the Remote 1, Remote 2, or

local temperature exceeds the programmed THERM limits. The

THERM temperature limits should normally be equal to or

greater than the high temperature limits. THERM is reset

automatically when the temperature falls back within the

(THERM − hysteresis) limit. The local and remote THERM

limits are set by default to 85°C. A hysteresis value can be

programmed, in which case, THERM resets when the

temperature falls to the limit value minus the hysteresis value.

This applies to both local and remote measurement channels.

The power-on hysteresis default value is 10°C, but this can be

reprogrammed to any value after power-up.

The hysteresis loop on the THERM outputs is useful when

THERM is used for on/off control of a fan. The system can be

set up so that when THERM asserts, a fan can be switched on to

cool the system. When THERM goes high again, the fan can be

switched off. Programming a hysteresis value protects from fan

jitter, where the temperature hovers around the THERM limit,

and the fan is constantly being switched on and off.

Table 17. THERM Hysteresis

THERM Hysteresis

Binary Representation

0°C

0 000 0000

1°C

0 000 0001

10°C

0 000 1010

If the ADT7482 is in the default temperature range (0°C to 127°C),

then THERM hysteresis must be less than the THERM limit.

Figure 21 shows how the THERM and ALERT outputs operate.

If desired, use the ALERT output as a SMBALERT to signal to

the host via the SMBus that the temperature has risen. Use the

THERM output to turn on a fan to cool the system, if the

temperature continues to increase. This method ensures that

there is a fail-safe mechanism to cool the system, without the

need for host intervention.

TEMPERATURE

100°C

90°C

80°C

70°C

60°C

50°C

40°C

THERM LIMIT

THERM LIMIT-HYSTERESIS

HIGH TEMP LIMIT

RESET BY MASTER

ALERT

1

4

THERM

2

3

Figure 21. Operation of the ALERT and THERM Interrupts

1. If the measured temperature exceeds the high temperature

limit, the ALERT output asserts low.

2. If the temperature continues to increase and exceeds the

THERM limit, the THERM output asserts low. This can be

used to throttle the CPU clock or switch on a fan.

3. The THERM output de-asserts (goes high) when the

temperature falls to THERM limit minus hysteresis. In

Figure 21, the default hysteresis value of 10°C is shown.

4. The ALERT output de-asserts only when the temperature

has fallen below the high temperature limit, and the master

has read the device address and cleared the status register.

Pin 8 on the ADT7482 can be configured as either an ALERT

output or as an additional THERM output. THERM2 asserts

low when the temperature exceeds the programmed local

and/or remote high temperature limits. It is reset in the same

manner as THERM, and it is not maskable. The programmed

hysteresis value applies to THERM2 also.

Figure 22 shows how THERM and THERM2 might operate

together to implement two methods of cooling the system. In

this example, the THERM2 limits are set lower than the

THERM limits. The THERM2 output could be used to turn on

a fan. If the temperature continues to rise and exceeds the

THERM limits, the THERM output could provide additional

cooling by throttling the CPU.

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