ADT7421ARMZ-2RL ON Semiconductor, ADT7421ARMZ-2RL Datasheet - Page 13

• 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

possibilities.
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•
Notes
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•
ALERT Output
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 pullup resistor. Several ALERT outputs can
be wire−OR’ed together, so that the common line goes low
if one or more of the ALERT outputs goes low.
processor, or 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.
common SMBALERT line that is connected to the master.
When the SMBALERT line is pulled low by one of the
devices, the following procedure occurs (see Figure 13):
When reading data from a register there are two
This is applicable when Pin 6 is configured as an ALERT
The ALERT output can be used as an interrupt signal to a
One or more ALERT outputs can be connected to a
If the address pointer register value of the ADT7421 is
unknown or not the desired value, it is first necessary to
set it to the correct value before data can be read from
the desired data register. This is done by writing to the
ADT7421 as before, but only the data byte containing
the register read address is sent, because data is not to
be written to the register (see Figure 11).
If the address pointer register is known to be at the
desired address, data can be read from the
corresponding data register without first writing to the
address pointer register and the bus transaction shown
in Figure 11 can be omitted.
It is possible to read a data byte from a data register
without first writing to the address pointer register.
However, if the address pointer register is already at the
correct value, it is not possible to write data to a register
without writing to the address pointer register because
the first data byte of a write is always written to the
address pointer register.
Some of the registers have different addresses for read
and write operations. The write address of a register
must be written to the address pointer if data is to be
written to that register, but it may not be possible to
read data from that address. The read address of a
register must be written to the address pointer before
data can be read from that register.
START
MASTER
RECEIVES
SMBALERT
A read operation is then performed consisting of the
serial bus address, R/W bit set to 1, followed by the
data byte read from the data register (see Figure 12).
ALERT RESPONSE
MASTER SENDS
ARA AND READ
Figure 13. Use of SMBALERT
ADDRESS
COMMAND
RD
ACK
DEVICE SENDS
ITS ADDRESS
ADDRESS
DEVICE
ACK
NO
http://onsemi.com
STOP
13
address, it resets its ALERT output, provided that the error
condition that caused the ALERT no longer exists. If the
SMBALERT line remains low, the master sends the ARA
again, and so on until all devices whose ALERT outputs
were low have responded.
Low Power Standby Mode
by setting Bit 6 of the configuration register. When Bit 6 is
low, the ADT7421 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. However, the SMBus is still enabled. Power
consumption in the standby mode is reduced to 10 mA.
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, 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 outside the new limits, an ALERT is generated,
even though the ADT7421 is still in standby.
Sensor Fault Detection
fault detection circuitry. This circuit can detect situations
where an external remote transistor is either not connected
or incorrectly connected to the ADT7421. 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.
ADT7421, tie the D+ and D− inputs together to prevent
continuous setting of the open flag.
Once the ADT7421 has responded to the alert response
The ADT7421 can be put into low power standby mode
When the device is in standby mode, it is possible to
At its D+ input, the ADT7421 contains internal sensor
If the user does not wish to use an external sensor with the
1. SMBALERT is pulled low.
2. Master initiates a read operation and sends the
3. The device whose ALERT output is low responds
4. If more than one device’s ALERT output is low,
alert response address (ARA = 0001 100). This is
a general call address that must not be used as a
specific device address.
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 it can be interrogated in
the usual way.
the one with the lowest device address takes
priority, in accordance with normal SMBus
arbitration.
DD
− 1.0 V