参数资料
型号: ADM1021A
厂商: Analog Devices, Inc.
英文描述: Low-Cost Microprocessor System Temperature Monitor
中文描述: 低成本的微处理器系统温度监控
文件页数: 5/12页
文件大小: 163K
代理商: ADM1021A
ADM1021A
–5–
REV. A
4
0
100k
2
FREQUENCY
Hz
T
10mV p-p
1M
10M
100M
1G
1
3
Figure 8. Temperature Error vs. Differential-Mode Noise
Frequency
CONVERSION RATE
Hz
250
0.125
S
0.25
0.5
8
300
350
400
550
4
0.0625
450
500
200
150
100
50
5 VOLTS
3.3 VOLTS
2
1
Figure 9. Operating Supply Current vs. Conversion Rate
0
20
SUPPLY VOLTAGE
V
0
S
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
40
60
80
100
20
Figure 10. Standby Supply Current vs. Supply Voltage
TIME
Seconds
T
0
25
50
75
100
125
REMOTE
TEMPERATURE
INT
TEMPERATURE
0
2
3
4
5
6
7
8
9
10
1
Figure 11. Response to Thermal Shock
FUNCTIONAL DESCRIPTION
The ADM1021A 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 ADM1021A
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, two's comple-
ment 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.
On initial power-up, the Remote and Local Temperature 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 out-
put. This may be cleared in one of two ways:
1.
Change both the local and remote lower limits to –128
°
C
and read the status register (which in turn clears the
ALERT output).
2.
Take the part out of standby and read the status register
(which in turn clears the ALERT output). This will work
only if the measured values are within the limit values.
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 V
BE
, which varies from device to device.
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