|
|
PDF ADM1021 Data sheet ( Hoja de datos )
| Número de pieza | ADM1021 | |
| Descripción | Low Cost Microprocessor System Temperature Monitor | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de ADM1021 (archivo pdf) en la parte inferior de esta página. Total 12 Páginas | ||
|
No Preview Available !
a
Low Cost Microprocessor
System Temperature Monitor
ADM1021
FEATURES
Improved Replacement for MAX1617
On-Chip and Remote Temperature Sensing
No Calibration Necessary
1؇C Accuracy for On-Chip Sensor
3؇C Accuracy for Remote Sensor
Programmable Over/Under Temperature Limits
Programmable Conversion Rate
2-Wire SMBus Serial Interface
Supports System Management Bus (SMBus™) Alert
70 A Max Operating Current
3 A Standby Current
3 V to 5.5 V Supply
Small 16-Lead QSOP Package
APPLICATIONS
Desktop Computers
Notebook Computers
Smart Batteries
Industrial Controllers
Telecomms Equipment
Instrumentation
PRODUCT DESCRIPTION
The ADM1021 is a two-channel digital thermometer and under/
over temperature alarm, intended for use in personal computers
and other systems requiring thermal monitoring and manage-
ment. The device can measure the temperature of a micropro-
cessor using a diode-connected PNP transistor, which may be
provided on-chip in the case of the Pentium® II or similar pro-
cessors, or can be a low cost discrete NPN/PNP device such as
the 2N3904/2N3906. A novel measurement technique cancels
out the absolute value of the transistor’s base emitter voltage, so
that no calibration is required. The second measurement chan-
nel measures the output of an on-chip temperature sensor, to
monitor the temperature of the device and its environment.
The ADM1021 communicates over a two-wire serial interface
compatible with SMBus standards. Under and over temperature
limits can be programmed into the devices over the serial bus,
and an ALERT output signals when the on-chip or remote
temperature is out of range. This output can be used as an inter-
rupt, or as an SMBus alert.
FUNCTIONAL BLOCK DIAGRAM
ON-CHIP TEMP.
SENSOR
LOCAL TEMPERATURE
VALUE REGISTER
D+
D–
ANALOG MUX
8-BIT A-TO-D
CONVERTER
BUSY RUN/STANDBY
REMOTE TEMPERATURE
VALUE REGISTER
EXTERNAL DIODE OPEN-CIRCUIT
LOCAL TEMPERATURE
LOW LIMIT COMPARATOR
LOCAL TEMPERATURE
HIGH LIMIT COMPARATOR
REMOTE TEMPERATURE
LOW LIMIT COMPARATOR
REMOTE TEMPERATURE
HIGH LIMIT COMPARATOR
STATUS REGISTER
ADDRESS POINTER
REGISTER
ONE-SHOT
REGISTER
CONVERSION RATE
REGISTER
LOCAL TEMPERATURE
LOW LIMIT REGISTER
LOCAL TEMPERATURE
HIGH LIMIT REGISTER
REMOTE TEMPERATURE
LOW LIMIT REGISTER
REMOTE TEMPERATURE
HIGH LIMIT REGISTER
CONFIGURATION
REGISTER
INTERRUPT
MASKING
STBY
ALERT
ADM1021
SMBUS INTERFACE
TEST VDD NC GND GND NC NC
TEST
SDATA
SCLK
ADD0
ADD1
SMBus is a trademark and Pentium is a registered trademark of Intel Corporation.
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1998
1 page  
10
9
8
7
10mV SQ. WAVE
6
5
4
3
2
1
0
50 500 5k 50k 100k 500k 5M 25M 50M
FREQUENCY – Hz
Figure 8. Temperature Error vs. Differential-Mode Noise
Frequency
ADM1021
100
ADDX = HI-Z
80
60
40
ADDX = GND
20
0
–20
0 1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.5 4.5
SUPPLY VOLTAGE – Volts
Figure 10. Standby Supply Current vs. Supply Voltage
200
180
160
140
120
100
80 VCC = +5V
60 VCC = +3.3V
40
20
0
0.0625 0.125 0.25
0.5
1
2
4
8
CONVERSION RATE – Hz
Figure 9. Operating Supply Current vs. Conversion
Rate
125
100
75
50
IMMERSED
25 IN +115؇C
FLUORINERT BATH
0
T=0
T=2
T=4
T=6
T=8
T = 10
TIME – Sec
Figure 11. Response to Thermal Shock
FUNCTIONAL DESCRIPTION
The ADM1021 contains a two-channel A-to-D converter with
special input-signal conditioning to enable operation with remote
and on-chip diode temperature sensors. When the ADM1021 is
operating normally, the A-to-D converter operates in a free-
running mode. The analog input multiplexer alternately selects
either the on-chip temperature sensor to measure its local tem-
perature, 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.
The measurement results are compared with Local and Remote,
High and Low Temperature Limits, stored in four on-chip regis-
ters. 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.
The limit registers can be programmed, and the device con-
trolled and configured, via the serial System Management Bus.
The contents of any register can also be read back via the SMBus.
Control and configuration functions consist of:
• Switching the device between normal operation and standby
mode.
• Masking or enabling the ALERT output.
• Selecting the conversion rate.
MEASUREMENT METHOD
A simple method of measuring temperature is to exploit the
negative temperature coefficient of a diode, or the base-emitter
voltage of a transistor, operated at constant current. Unfortu-
nately, this technique requires calibration to null out the effect
of the absolute value of Vbe, which varies from device to device.
The technique used in the ADM1021 is to measure the change
in Vbe when the device is operated at two different currents.
This is given by:
where:
∆Vbe = KT/q × ln (N)
K is Boltzmann’s constant
q is charge on the electron (1.6 x 10–19 Coulombs)
T is absolute temperature in Kelvins
N is ratio of the two currents
REV. 0
–5–
5 Page 
ADM1021
APPLICATIONS INFORMATION
FACTORS AFFECTING ACCURACY
Remote Sensing Diode
The ADM1021 is designed to work with substrate transistors
built into processors, or with discrete transistors. Substrate
transistors will generally be PNP types with the collector con-
nected 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 then the collector and base are con-
nected to D+ and the emitter to D–. If a PNP transistor is used
then the collector and base are connected to D– and the emitter
to D+.
The user has no choice in the case of substrate transistors, but if
a discrete transistor is used the best accuracy will be obtained by
choosing devices according to the following criteria:
1. Base-emitter voltage greater than 0.25 V at 6 µA, at the high-
est operating temperature.
2. Base-emitter voltage less than 0.95 V at 100 µA, at the lowest
operating temperature.
3. Base resistance less than 100 Ω.
4. Small variation in hfe (say 50 to 150) which indicates tight
control of Vbe characteristics.
Transistors such as 2N3904, 2N3906 or equivalents in SOT-23
package are suitable devices to use.
Thermal Inertia and Self-Heating
Accuracy depends on the temperature of the 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 will cause a lag in the response of the sensor to a
temperature change. In the case of the remote sensor this should
not be a problem, as it will be either a substrate transistor in the
processor or a small package device such as SOT-23 placed in
close proximity to it.
The on-chip sensor, however, will often be remote from the
processor and will only be monitoring the general ambient tem-
perature around the package. The thermal time constant of the
QSOP-16 package is about 10 seconds.
In practice, the package will have electrical, and hence thermal,
connection to the printed circuit board, so the temperature rise
due to self-heating will be negligible.
LAYOUT CONSIDERATIONS
Digital boards can be electrically noisy environments, and the
ADM1021 is measuring very small voltages from the remote
sensor, so care must be taken to minimize noise induced at the
sensor inputs. The following precautions should be taken:
1. Place the ADM1021 as close as possible to the remote sens-
ing 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.
2. Route the D+ and D– tracks close together, in parallel, with
grounded guard tracks on each side. Provide a ground plane
under the tracks if possible.
3. Use wide tracks to minimize inductance and reduce noise
pickup. 10 mil track minimum width and spacing is recom-
mended.
GND
D+
D-
GND
10 mil.
10 mil.
10 mil.
10 mil.
10 mil.
10 mil.
10 mil.
Figure 17. Arrangement of Signal Tracks
4. Try to minimize the number of copper/solder joints, which
can cause thermocouple effects. Where copper/solder joints
are used, make sure that they are in both the D+ and D–
path and at the same temperature.
Thermocouple effects should not be a major problem as 1°C
corresponds to about 240 µV, and thermocouple voltages are
about 3 µV/°C of temperature difference. Unless there are
two thermocouples with a big temperature differential be-
tween them, thermocouple voltages should be much less
than 240 µV.
5. Place a 0.1 µF bypass capacitor close to the VDD pin and
2200 pF input filter capacitors across D+, D– close to the
ADM1021.
6. If the distance to the remote sensor is more than eight inches,
the use of twisted pair cable is recommended. This will work
up to about 6 to 12 feet.
7. For really long distances (up to 100 feet), use shielded twisted
pair such as Belden #8451 microphone cable. Connect the
twisted pair to D+ and D– and the shield to GND close to
the ADM1021. Leave the remote end of the shield uncon-
nected to avoid ground loops.
Because the measurement technique uses switched current
sources, excessive cable and/or filter capacitance can affect the
measurement. When using long cables, the filter capacitor may
be reduced or removed.
Cable resistance can also introduce errors. 1 Ω series resistance
introduces about 0.5°C error.
REV. 0
–11–
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet ADM1021.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| ADM1020 | 8-Lead/ Low-Cost/ System Temperature Monitor | Analog Devices |
| ADM1021 | Low Cost Microprocessor System Temperature Monitor | Analog Devices |
| ADM1021A | Low Cost Microprocessor System Temperature Monitor Microcomputer |  ON Semiconductor |
| ADM1021A | System Temperature Monitor Microcomputer | Analog Devices |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |