ADT7461ARMZ-2REEL7 ON Semiconductor, ADT7461ARMZ-2REEL7 Datasheet - Page 15

• Manufacturer Part Number: ADT7461ARMZ-2REEL7
• Description: IC SENSOR TEMP DGTL 2CH 8MSOP
• Manufacturer: ON Semiconductor

Specifications of ADT7461ARMZ-2REEL7

• Function: Temp Monitoring System (Sensor)
• Topology: ADC, Comparator, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: 0°C ~ 127°C, External Sensor
• Output Type: SMBus™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 120°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Sensor Fault Detection
fault detection circuitry. This circuit can detect situations
where an external remote diode is either not connected or
incorrectly connected to the ADT7461. A simple voltage
comparator trips if the voltage at D+ exceeds V
(typical), signifying an open circuit between D+ and D−.
The output of this comparator is checked when a conversion
is initiated. Bit 2 of the status register (open flag) is set if a
fault is detected. If the ALERT pin is enabled, setting this
flag causes ALERT to assert low.
ADT7461, then to prevent continuous setting of the OPEN
flag, the user should tie the D+ and D− inputs together.
The ADT7461 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 diode. 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 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.
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 limit is set by default to 85°C,
as is the local THERM limit. A hysteresis value can be
programmed so that 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 powerup.
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
hovers around the THERM limit, and the fan is constantly
being switched.
Table 9. THERM Hysteresis
At its D+ input, the ADT7461 contains internal sensor
If the user does not wish to use an external sensor with the
The ADT7461 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
THERM Hysteresis
value protects from fan jitter where the temperature
10°C
0°C
1°C
Binary Representation
0 000 0000
0 000 0001
0 000 1010
DD
http://onsemi.com
−1 V
15
operate. A user may choose to use the ALERT output as an
SMBALERT to signal to the host via the SMBus that the
temperature has risen. The user could use the THERM
output to turn on a fan to cool the system, if the temperature
continues to increase. This method would ensure 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
Figure 20 shows how the THERM and ALERT outputs
THERM
ALERT
Figure 20. Operation of the ALERT and THERM
1. If the measured temperature exceeds the high
2. If the temperature continues to increase and
3. The THERM output deasserts (goes high) when
4. The ALERT output deasserts only when the
temperature limit, the ALERT output asserts low.
exceeds the THERM limit, the THERM output
asserts low. This can be used to throttle the CPU
clock or switch on a fan.
the temperature falls to THERM limit minus
hysteresis. The default hysteresis value of 10°C is
shown in Figure 20.
temperature falls below the high temperature limit,
and the master has read the device address and
cleared the status register.
Pin 6 on the ADT7461 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 21 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.
1
2
Interrupts
3
RESET BY MASTER
THERM LIMIT
THERM LIMIT−HYSTERESIS
HIGH TEMP LIMIT
4