ADM1021AARQ ON Semiconductor, ADM1021AARQ Datasheet - Page 7

• Manufacturer Part Number: ADM1021AARQ
• Description: IC SENSOR TEMP DUAL3/5.5V 16QSOP
• Manufacturer: ON Semiconductor

Specifications of ADM1021AARQ

• 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

Functional Description
converter with special input−signal conditioning to enable
operation with remote and on−chip diode temperature
sensors. When the ADM1021A is operating normally, the
A−to−D converter operates in free−running mode. The
analog input multiplexer alternately selects either the
on−chip temperature sensor to measure its local temperature
or the remote temperature sensor. These signals are digitized
by the ADC and the results stored in the local and remote
temperature value registers as 8−bit, twos complement
words.
remote, high and low temperature limits, stored in four
on−chip registers. Out−of−limit comparisons generate flags
that are stored in the status register, and one or more
out−of−limit results will cause the ALERT output to pull low.
controlled and configured via the serial System
Management Bus (SMBus). The contents of any register can
also be read back via the SMBus.
•
•
•
change in V
currents. This is given by:
measure the output of an external temperature sensor.
The ADM1021A contains a two−channel A−to−D
The measurement results are compared with local and
The limit registers can be programmed and the device
Control and configuration functions consist of:
The technique used in the ADM1021A is to measure the
where:
Figure 13 shows the input signal conditioning used to
Switching the device between normal operation and
standby mode.
Masking or enabling the ALERT output.
Selecting the conversion rate.
K is Boltzmann’s constant.
q is the charge on the electron (1.6 × 10
T is the absolute temperature in Kelvins.
N is the ratio of the two currents.
BE
TRANSISTOR
SENSING
REMOTE
when the device is operated at two different
DV
BE
+ KT q
C1*
D+
D–
1n ( N )
I
Figure 13. Input Signal Conditioning
–19
DIODE
Coulombs).
BIAS
N y 1
(eq. 1)
http://onsemi.com
I
ADM1021A
BIAS
LOW−PASS FILTER
f
7
C
* CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS.
= 65kHz
C1 = 2.2nF TYP, 3nF MAX.
values default to –128°C. Since the device normally powers
up converting, a measurement of local and remote
temperature is made, and these values are then stored before
a comparison with the stored limits is made. However, if the
part is powered up in standby mode (STBY pin pulled low),
no new values are written to the register before a comparison
is made. As a result, both RLOW and LLOW are tripped in
the status register, thus generating an ALERT output. This
can be cleared in one of two ways.
Measurement Method
the negative temperature coefficient of a diode, or the
base−emitter voltage of a transistor, operated at constant
current. Unfortunately, this technique requires calibration to
null the effect of the absolute value of V
from device to device.
transistor provided for temperature monitoring on some
microprocessors, but it could be a discrete transistor. If a
discrete transistor is used, the collector will not be grounded
and should be linked to the base. To prevent ground noise
interfering with the measurement, the more negative
terminal of the sensor is not referenced to ground, but is
biased above ground by an internal diode at the D– input. If
the sensor is operating in a noisy environment, one can
optionally be added as a noise filter. Its value is typically
2200 pF, but it should be no more than 3000 pF. See the
Layout Considerations section for more information.
V
DD
On initial powerup, the remote and local temperature
A simple method of measuring temperature is to exploit
This figure shows the external sensor as a substrate
1. Change both the local and remote lower limits to
2. Take the part out of standby and read the status
–128°C and read the status register (which in turn
clears the ALERT output).
register (which in turn clears the ALERT output).
This works only if the measured values are within
the limit values.
TO ADC
V
V
OUT–
OUT+
BE,
which varies