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PDF ADM1020 Data sheet ( Hoja de datos )
| Número de pieza | ADM1020 | |
| Descripción | 8-Lead/ Low-Cost/ System Temperature Monitor | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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a
8-Lead, Low-Cost, System
Temperature Monitor
ADM1020
FEATURES
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 SMBus Alert
70 A Max Operating Current
3 A Standby Current
+3 V to +5.5 V Supply
8-Lead SOIC Package
PRODUCT DESCRIPTION
The ADM1020 is a two-channel digital thermometer and
under/over temperature alarm, intended for use in personal
computers and other systems requiring thermal monitoring and
management. The device can measure the temperature of a
microprocessor using a diode-connected NPN or PNP transis-
tor, which may be provided on-chip in the case of the Pentium®
II or similar processors, or can be a low-cost discrete device
such as the 2N3904. 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.
APPLICATIONS
Desktop Computers
Notebook Computers
Smart Batteries
Industrial Controllers
Telecommunication Equipment
Instrumentation
The ADM1020 communicates over a two-wire serial interface
compatible with System Management Bus (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 interrupt, or as an SMBus alert.
FUNCTIONAL BLOCK DIAGRAM
ON-CHIP TEMP.
SENSOR
LOCAL TEMPERATURE
VALUE REGISTER
D+
ANALOG
8-BIT A-TO-D
D–
MUX
CONVERTER
BUSY RUN/STANDBY
REMOTE TEMPERATURE
VALUE REGISTER
EXTERNAL DIODE OPEN-CIRCUIT
ADM1020
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
SMBUS INTERFACE
ALERT
VDD GND
SDATA
SCLK
ADD
SMBus is a trademark of Intel Corporation.
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., 1999
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 7. Temperature Error vs. Differential-Mode Noise
Frequency
ADM1020
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 9. 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 8. 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 10. Response to Thermal Shock
FUNCTIONAL DESCRIPTION
The ADM1020 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
ADM1020 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
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.
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
(SMBus). 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 ADM1020 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 × 10–19 Coulombs).
T is absolute temperature in Kelvins.
N is ratio of the two currents.
REV. 0
–5–
5 Page 
ADM1020
LAYOUT CONSIDERATIONS
Digital boards can be electrically noisy environments, and the
ADM1020 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 ADM1020 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 4 to 8 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
recommended.
GND
D+
D–
GND
10mil
10mil
10mil
10mil
10mil
10mil
10mil
Figure 14. 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 should not be a major
problem as 1°C corresponds to about 200 mV, and thermo-
couple voltages are about 3 mV/°C of temperature difference.
Unless there are two thermocouples with a big temperature
differential between them, thermocouple voltages should be
much less than 200 mV.
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
ADM1020.
6. If the distance to the remote sensor is more than 8 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 ADM1020. 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.
APPLICATION CIRCUITS
Figure 15 shows a typical application circuit for the ADM1020,
using a discrete sensor transistor connected via a shielded,
twisted pair cable. The pull-ups on SCLK, SDATA and ALERT
are required only if they are not already provided elsewhere in
the system.
VDD
ADM1020
2N3904
C1*
SHIELD
D+
D–
SCLK
SDATA
ALERT
0.1F
10k⍀
10k⍀
+3.3V
10k⍀
IN
TO
I/O PIIX4
CHIP
OUT
*C1 IS OPTIONAL
ADD
GND
SET TO REQUIRED
ADDRESS
Figure 15. Typical ADM1020 Application Circuit
REV. 0
–11–
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet ADM1020.PDF ] | |
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