ADT7461AR-REEL7 ON Semiconductor, ADT7461AR-REEL7 Datasheet - Page 17

• Manufacturer Part Number: ADT7461AR-REEL7
• Description: IC SENSOR TEMP 2-CH 8SOIC
• Manufacturer: ON Semiconductor

Specifications of ADT7461AR-REEL7

• Rohs Status: RoHS non-compliant
• 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-SOIC (3.9mm Width)

ALERT OUTPUT
This is applicable when Pin 6 is configured as an ALERT
output. The ALERT output goes low whenever an out-of-limit
measurement is detected, or if the remote temperature sensor is
open circuit. It is an open-drain output and requires a pull-up
to V
the common line goes low if one or more of the ALERT outputs
goes low.
The ALERT output can be used as an interrupt signal to a
processor, or it may be used as an SMBALERT. Slave devices on
the SMBus cannot normally signal to the bus master that they
want to talk, but the SMBALERT function allows them to do so.
One or more ALERT outputs can be connected to a common
SMBALERT line that is connected to the master. When the
SMBALERT line is pulled low by one of the devices, the
procedure shown in Figure 20 occurs.
1.
2.
3.
4.
5.
START
MASTER
RECEIVES
SMBALERT
DD
SMBALERT is pulled low.
Master initiates a read operation and sends the alert
response address (ARA = 0001 100). This is a general call
address that must not be used as a specific device address.
The device whose ALERT output is low responds to the
alert response address and the master reads its device
address. As the device address is seven bits, an LSB of 1 is
added. The address of the device is now known and can be
interrogated in the usual way.
If the ALERT output is low on more than one device, the
one with the lowest device address has priority, in
accordance with normal SMBus arbitration.
Once the ADT7461 has responded to the alert response
address, it resets its ALERT output, provided the error
condition that caused the ALERT no longer exists. If the
SMBALERT line remains low, the master sends the ARA
again; this sequence continues until all devices whose
ALERT out-puts were low have responded.
. Several ALERT outputs can be wire-ORed together, so
ALERT RESPONSE
MASTER SENDS
ARA AND READ
ADDRESS
COMMAND
Figure 20. Use of SMBALERT
RD
ACK
DEVICE SENDS
ITS ADDRESS
ADDRESS
DEVICE
ACK
NO
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STOP
LOW POWER STANDBY MODE
The ADT7461 can be put into low power standby mode by set-
ting Bit 6 of the configuration register. When Bit 6 is low, the
ADT7461 operates normally. When Bit 6 is high, the ADC is
inhibited, and any conversion in progress is terminated without
writing the result to the corresponding value register.
The SMBus is still enabled. Power consumption in the standby
mode is reduced to less than 10 μA if there is no SMBus activity
or 100 μA if there are clock and data signals on the bus.
When the device is in standby mode, it is still possible to initiate
a one-shot conversion of both channels by writing to the one-
shot register (Address 0x0F), after which the device returns to
standby. It does not matter what is written to the one-shot
register, as all data written to it is ignored. It is also possible to
write new values to the limit register while in standby mode. If
the values stored in the temperature value registers are now
outside the new limits, an ALERT is generated even though the
ADT7461 is still in standby.
SENSOR FAULT DETECTION
At its D+ input, the ADT7461 contains internal sensor 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
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.
If the user does not wish to use an external sensor with the
ADT7461, then to prevent continuous setting of the OPEN flag,
the user should tie the D+ and D− inputs together.
THE ADT7461 INTERRUPT SYSTEM
The ADT7461 has two interrupt outputs, ALERT and THERM.
Both have different functions and behavior. ALERT is maskable
and responds to violations of software-programmed tempera-
ture limits or an open-circuit fault on the external diode.
THERM is intended as a fail-safe interrupt output that cannot
be masked.
If the external or local temperature exceeds the programmed
high temperature limits or equals or exceeds the low tempera-
ture 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.
The THERM output asserts low if the external or local tempera-
ture exceeds the programmed THERM limits. THERM
temperature limits should normally be equal to or greater than
DD
−1 V (typical), signifying an
ADT7461