參數(shù)資料
型號(hào)： ICL7149CPL
廠商： HARRIS SEMICONDUCTOR
元件分類： 模擬信號(hào)調(diào)理
英文描述： 33/4 Digit, Autoranging Multimeter
中文描述： SPECIALTY ANALOG CIRCUIT, PDIP40
文件頁(yè)數(shù)： 9/13頁(yè)
文件大?。?/td> 111K
代理商： ICL7149CPL
3-41
Ratiometric
Measurement
The ratiometric
measurement is performed by first
integrating the voltage across an unknown resistor, R
X
, then
effectively deintegrating the voltage across a known resistor
(R
KNOWN1
or R
KNOWN2
of Figure 8). The shunting effect of
R
INTV
does not affect the reading because it cancels exactly
between integration and deintegration. Like the current mea-
surements, the
measurements are split into two sets of
ranges. LO
measurements use a 10k
reference resistor,
and the full scale ranges are 4k
and 40k
. HI
measure-
ments use a 1M
reference resistor, and the full scale ranges
are 0.4M
and 4M
. The measurement phases and timing
are the same as the measurement phases and timing for DC
current except: 1) During the integrate phases the input volt-
age is the voltage across the unknown resistor R
X
, and; 2)
During the deintegrate phases, the input voltage is the voltage
across the reference resistor R
KNOWN1
or R
KNOWN2
.
Continuity Indication
When the ICL7139 and ICL7149 are in the LO
measurement mode, the continuity circuit of Figure 9 will be
active. When the voltage across R
X
is less than approximately
100mV, the beeper output will be on. When R
KNOWN
is 10k
,
the beeper output will be on when R
X
is less than 1k
.
Common Voltage
The analog and digital common voltages of the ICL7139 and
ICL7149 are generated by an on-chip resistor/zener/diode
combination, shown in Figure 10. The resistor values are
chosen so the coefficient of the diode voltage cancels the
positive temperature coefficient of the zener voltage. This
voltage is then buffered to provide the analog common and
the digital common voltages. The nominal voltage between
V+ and analog common is 3V. The analog common buffer
can sink about 20mA, or source 0.01mA, with an output
impedance of 10
. A pullup resistor to V+ may be used if
more sourcing capability is desired. Analog common may be
used to generate the reference voltage, if desired.
Oscillator
The ICL7139 and ICL7149 use a parallel resonant-type
crystal in a Pierce oscillator configuration, as shown in
Figure 11, and requires no other external components. The
crystal eliminates the need to trim the oscillator frequency.
An external signal may be capacitively coupled in OSC IN,
with a signal level between 0.5V and 3V
P-P
. Because the
+
-
+
-
+
-
TRIPLE
POINT
C
AZ
C
INT
R
DEINT
AZ
INTEGRATOR
COMPARATOR
TO LOGIC SECTION
COMMON
R
INTV
INT V/
C
AZ
C
INT
R
DEINT
AZ
AZ
AZ
T
T
DEINT+
DEINT+
T = INT + DEINT
AZ = AUTOZERO
INT = INTEGRATE
V
REF
LOW
+
-
LOW
LO
HI
R
KNOWN 1
R
KNOWN 2
R
X
FIGURE 8. DETAILED CIRCUIT DIAGRAM FOR RATIOMETRIC
MEASUREMENT
+
-
COM
LO
HI
+
-
+
-
R
KNOWN
V
X
BEEPER
OUTPUT
R
UNKNOWN
V
REF
LO
2kHz
V+
V+
V
X
= 100mV
R
X
FIGURE 9. CONTINUITY BEEPER DRIVE CIRCUIT
+
-
P
+
-
P
0.3V
+
-
LOGIC
SECTION
V+
LO BAT
DIGITAL
COMMON
(INTERNAL)
3.1V
+
+
3V
-
ANALOG
COMMON
(PIN 10)
V-
6.7V
125K
5K
180K
80
μ
A
FIGURE 10. ANALOG AND DIGITAL COMMON VOLTAGE
GENERATOR CIRCUIT
+
-
ICL7139, ICL7149
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