ADM1021AARQ-REEL7 ON Semiconductor, ADM1021AARQ-REEL7 Datasheet - Page 13

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ADM1021AARQ-REEL7

Manufacturer Part Number
ADM1021AARQ-REEL7
Description
IC SENSOR TEMP DUAL3/5.5V 16QSOP
Manufacturer
ON Semiconductor
Datasheet

Specifications of ADM1021AARQ-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 ~ 100°C, External Sensor
Output Type
SMBus™
Output Alarm
Yes
Output Fan
No
Voltage - Supply
3 V ~ 5.5 V
Operating Temperature
0°C ~ 100°C
Mounting Type
Surface Mount
Package / Case
16-QSOP
Low Power Standby Modes
mode using hardware or software, that is, by taking the
STBY input low, or by setting Bit 6 of the configuration
register. When STBY is high or Bit 6 is low, the ADM1021A
operates normally. When STBY is pulled low or Bit 6 is
high, the ADC is inhibited, so any conversion in progress is
terminated without writing the result to the corresponding
value register.
standby mode is reduced to less than 10 mA if there is no
SMBus activity or 100 mA if there are clock and data signals
on the bus.
STBY is low, conversions are completely inhibited. When
Bit 6 is set but STBY is high, a one−shot conversion of both
channels can be initiated by writing 0xXX to the one−shot
register (Address 0x0F).
Sensor Fault Detection
detects if the external sensor diode is open−circuit. This is a
simple voltage comparator that trips if the voltage at D+
exceeds V
is checked when a conversion is initiated and sets Bit 2 of the
status register if a fault is detected.
measuring range, for example due to the diode being
short−circuited, the ADC outputs −128°C (1000 0000).
Since the normal operating temperature range of the device
only extends down to 0°C, this output code is never seen in
normal operation; therefore, it can be interpreted as a fault
condition.
upon competitive devices that output 0 if the external sensor
goes short−circuit. These devices can misinterpret a genuine
0°C measurement as a fault condition.
shorted out, the resulting ALERT can be cleared by writing
0x80 (−128°C) to the low limit register.
Factors Affecting Accuracy
Remote Sensing Diode
transistors built into processors, or with discrete transistors.
Substrate transistors are generally PNP types with the
collector connected to the substrate. Discrete types can be
either PNP or NPN, connected as a diode (base shorted to
collector). If an NPN transistor is used, the collector and
The ADM1021A can be put into a low power standby
The SMBus is still enabled. Power consumption in the
These two modes are similar but not identical. When
The ADM1021A has a fault detector at the D+ input that
If the remote sensor voltage falls below the normal
In this respect, the ADM1021A differs from and improves
If the external diode channel is not being used and is
The ADM1021A is designed to work with substrate
5. Once the ADM1021A has responded to the alert
response 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.
CC
– 1.0 V (typical). The output of this comparator
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ADM1021A
13
base are connected to D+ and the emitter to D−. If a PNP
transistor is used, the collector and base are connected to D−
and the emitter to D+.
but if a discrete transistor is used, the best accuracy is
obtained by choosing devices according to the following
criteria:
SOT−23 package are suitable devices to use.
Thermal Inertia and Self−Heating
remote−sensing diode and/or the internal temperature sensor
being at the same temperature as that being measured, and a
number of factors can affect this. Ideally, the sensor should be
in good thermal contact with the part of the system being
measured, for example the processor. If it is not, the thermal
inertia caused by the mass of the sensor causes a lag in the
response of the sensor to a temperature change. For the
remote sensor, this should not be a problem, because it is
either a substrate transistor in the processor or a small package
device, such as SOT−23, placed in close proximity to it.
processor and only monitors the general ambient
temperature around the package. The thermal time constant
of the QSOP−16 package is approximately 10 seconds.
a thermal, connection to the printed circuit board, so the
temperature rise due to self−heating is negligible.
Layout Considerations
because the ADM1021A is measuring very small voltages
from the remote sensor, care must be taken to minimize
noise induced at the sensor inputs. The following
precautions should be taken:
The user has no choice in the case of substrate transistors,
Transistors, such as 2N3904, 2N3906, or equivalents, in
Accuracy
The on−chip sensor is, however, often remote from the
In practice, the package will have an electrical, and hence
Digital boards can be electrically noisy environments, and
1. Base−emitter voltage greater than 0.25 V at 6 mA,
2. Base−emitter voltage less than 0.95 V at 100 mA,
3. Base resistance less than 100 W.
4. Small variation in h
1. Place the ADM1021A as close as possible to the
2. Route the D+ and D− tracks close together, in
3. Use wide tracks to minimize inductance and
4. Try to minimize the number of copper/solder
at the highest operating temperature.
at the lowest operating temperature.
indicates tight control of V
remote sensing diode. Provided that the worst
noise sources, such as clock generators,
data/address buses, and CRTs, are avoided, this
distance can be four to eight inches.
parallel, with grounded guard tracks on each side.
Provide a ground plane under the tracks, if
possible.
reduce noise pickup. 10 mil track minimum width
and spacing is recommended.
joints, which can cause thermocouple effects.
depends
on
FE
(such as 50 to 150), which
the
BE
temperature
characteristics.
of
the

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