ADT7483AARQZ-REEL ON Semiconductor, ADT7483AARQZ-REEL Datasheet - Page 20

• Manufacturer Part Number: ADT7483AARQZ-REEL
• Description: IC TEMP SENSOR/ALARM 3CH 16-QSOP
• Manufacturer: ON Semiconductor

Specifications of ADT7483AARQZ-REEL

• Function: Temp Monitoring System (Sensor)
• Topology: ADC, Comparator, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: SMBus™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 3.6 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADT7483A
registers are now outside the new limits, an ALERT is
generated, even though the ADT7483A is still in standby.
SENSOR FAULT DETECTION
The ADT7483A has internal sensor fault detection circuitry
located at its D+ input. This circuit can detect situations where
a remote diode is not connected, or is incorrectly connected, to
the ADT7483A. A simple voltage comparator trips if the voltage
at D+ exceeds V
between D+ and D−. The output of this comparator is checked
when a conversion is initiated. Bit 2 (D1 OPEN flag) of the
Status Register 1 (Address 0x02) is set if a fault is detected on
the Remote 1 channel. Bit 2 (D2 OPEN flag) of the Status
Register 2 (Address 0x23) is set if a fault is detected on the
Remote 2 channel. If the ALERT pin is enabled, setting this flag
will cause ALERT to assert low.
If a remote sensor is not used with the ADT7483A, then the D+
and D− inputs of the ADT7483A need to be tied together to
prevent the OPEN flag from being continuously set.
Most temperature sensing diodes have an operating temperature
range of −55°C to +150°C. Above 150°C, they lose their
semiconductor characteristics and approximate conductors
instead. This results in a diode short, setting the OPEN flag. The
remote diode in this case no longer gives an accurate temperature
measurement. A read of the temperature result register will give
the last good temperature measurement. The user should be
aware that, while the diode fault is triggered, the temperature
measurement on the remote channels may not be accurate.
INTERRUPT SYSTEM
The ADT7483A has two interrupt outputs, ALERT and
THERM. Both outputs have different functions and behavior.
ALERT is maskable and responds to violations of software
programmed temperature limits or an open-circuit fault on the
remote diode. THERM is intended as a fail-safe interrupt
output that cannot be masked.
If the Remote 1, Remote 2, or local temperature exceeds the
programmed high temperature limits, or equals or exceeds the
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.
DD
− 1 V (typical), signifying an open circuit
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Similarly, 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 automatically reset when the temperature
falls back within the (THERM − Hysteresis) limit. The local and
remote THERM limits are set by default to 85°C. An 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
may 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 user’s 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 an hysteresis value
protects from fan jitter, wherein the temperature hovers around
the THERM limit and the fan is constantly being switched.
Table 17. THERM Hysteresis
THERM Hysteresis
0°C
1°C
10°C
Figure 20 shows how the THERM and ALERT outputs operate.
The ALERT output can be used as an SMBALERT to signal to
the host via the SMBus that the temperature has risen. If the
temperature continues to increase, the THERM output can be
used to turn on a fan to cool the system. This method ensures
that there is a fail-safe mechanism to cool the system, without
the need for host intervention.
TEMPERATURE
THERM
ALERT
100°C
90°C
80°C
70°C
60°C
50°C
40°C
Figure 20. Operation of the ALERT and THERM Outputs
1
2
3
Binary Representation
0 000 0000
0 000 0001
0 000 1010
RESET BY MASTER
4
THERM LIMIT
THERM LIMIT-HYSTERESIS
HIGH TEMP LIMIT