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ADM1021 Datasheet(PDF) 5 Page - Analog Devices

Part No. ADM1021
Description  Low Cost Microprocessor System Temperature Monitor
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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ADM1021 Datasheet(HTML) 5 Page - Analog Devices

 
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ADM1021
–5–
REV. 0
FREQUENCY – Hz
10
0
50
50M
500
5k
50k
500k
5M
6
5
4
2
1
3
10mV SQ. WAVE
9
8
7
100k
25M
Figure 8. Temperature Error vs. Differential-Mode Noise
Frequency
CONVERSION RATE – Hz
200
0
0.0625
8
0.125
0.25
0.5
1
2
4
180
80
60
40
20
140
100
160
120
VCC = +5V
VCC = +3.3V
Figure 9. Operating Supply Current vs. Conversion
Rate
SUPPLY VOLTAGE – Volts
100
40
–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
80
60
20
0
ADDX = HI-Z
ADDX = GND
Figure 10. Standby Supply Current vs. Supply Voltage
TIME – Sec
125
100
0
T = 0
T = 10
T = 2
T = 4
T = 6
T = 8
75
50
25
IMMERSED
IN +115 C
FLUORINERT BATH
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:
∆V
be = KT/q × ln (N)
where:
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


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