ADT7421ARMZ-2RL ON Semiconductor, ADT7421ARMZ-2RL Datasheet - Page 14

• Manufacturer Part Number: ADT7421ARMZ-2RL
• Description: IC TEMP MONITOR 8-MSOP
• Manufacturer: ON Semiconductor
• Type: Temperature Sensorr

Specifications of ADT7421ARMZ-2RL

• Input Type: Logic
• Output Type: Logic
• Interface: 2-Wire SMBus
• Current - Supply: 4mA
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Full Temp Accuracy: +/- 2.75 C, +/- 3.25 C
• Digital Output - Bus Interface: Serial (2-Wire)
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: 0 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The ADT7421 Interrupt System
THERM. Both have different functions and behavior.
ALERT is maskable and responds to violations of software
programmed temperature limits or an open−circuit fault on
the external transistor. THERM is intended as a fail−safe
interrupt output that cannot be masked.
programmed high temperature limits, or equals or exceeds the
low temperature limits, the ALERT output is asserted low. An
open−circuit fault on the external transistor 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.
temperature exceeds the programmed THERM limits.
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 limit. The external and local 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 between 0°C and 31°C after powerup.
THERM is used, for example, as an on/off controller for a
fan. The user’s system can be set up so that when THERM
asserts, a fan is 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 switched.
Table 9. THERM Hysteresis
operate. The ALERT output can be used as a SMBALERT
to signal to the host via the SMBus that the temperature has
risen. The user can 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.
The ADT7421 has two interrupt outputs, ALERT and
If the external or local temperature exceeds the
The THERM output asserts low if the external or local
The hysteresis loop on the THERM outputs is useful when
Figure 14 shows how the THERM and ALERT outputs
THERM Hysteresis
10°C
0°C
1°C
Binary Representation
0 000 0000
0 000 0001
0 000 1010
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•
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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 is used to turn on a
fan. If the temperature continues to rise and exceeds the
THERM limits, the THERM output provides additional
cooling by throttling the CPU.
1005C
THERM
ALERT
905C
805C
705C
605C
505C
405C
THERM2
Figure 15 shows how THERM and THERM2 operate
If the measured temperature exceeds the high
temperature limit, the ALERT output asserts low.
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.
The THERM output de−asserts (goes high) when the
temperature falls to THERM limit minus hysteresis. In
Figure 14, the default hysteresis value of 10°C is shown.
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 6 on the ADT7421 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 is
not maskable.
The programmed hysteresis value also applies to
THERM2.
905C
805C
705C
605C
505C
405C
305C
THERM
Figure 15. Operation of the THERM and THERM2
Figure 14. Operation of the ALERT and THERM
TEMPERATURE
TEMPERATURE
1
1
2
2
Interrupts
Interrupts
3
3
RESET BY MASTER
4
4
THERM LIMIT
THERM LIMIT−
HIGH TEMP LIMIT
THERM LIMIT
THERM2 LIMIT
HYSTERESIS