CA5420A 查看數據表（PDF） - Intersil
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CA5420A Datasheet PDF : 8 Pages
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CA5420A
Typical Applications
Picoammeter Circuit
The exceptionally low input current (typically 0.2pA) makes
the CA5420A highly suited for use in a picoammeter circuit.
With only a single 10GΩ resistor, this circuit covers the range
from ±1.5pA. Higher current ranges are possible with suitable
switching techniques and current scaling resistors. Input
transient protection is provided by the 1MΩ resistor in series
with the input. Higher current ranges require that this resistor
be reduced. The 10MΩ resistor connected to pin 2 of the
CA5420A decouples the potentially high input capacitance
often associated with lower current circuits and reduces the
tendency for the circuit to oscillate under these conditions.
10GΩ
1MΩ
10MΩ
10pF +1.5V
2-
7
CA5420A 6
500-0-500
µA
M
3+
4
5
1
BATTERY
RETURNS
10kΩ
±50pA
±15pA
-1.5V
±5pA
±1.5pA
1.5kΩ
1.5kΩ
1%
1kΩ
430Ω
1%
150Ω
1%
11kΩ
68Ω
1%
High Input Resistance Voltmeter
Advantage is taken of the high input impedance of the
CA5420A in a high input resistance DC voltmeter. Only two
1.5V “AA” type penlite batteries power this exceedingly
high-input resistance (>1,000,000MΩ) DC voltmeter. Full-scale
deflection is ±500mV, ±150mV, and ±15mV. Higher voltage
ranges are easily added with external input voltage attenuator
networks.
The meter is placed in series with the gain network, thus
eliminating the meter temperature co-efficient error term.
Supply current in the standby position with the meter
undeflected is 300µA. At full-scale deflection this current
rises to 800µA. Carbon-zinc battery life should be in excess
of 1,000 hours.
+1.5V
22MΩ
3+
7
10MΩ
CA5420A 6
500-0-500
µA
M
100pF
2
-
4
±500mV
5
1
BATTERY
RETURNS
10kΩ
±150mV
-1.5V
±50mV
±15mV
1.5kΩ
1.5kΩ
1%
1kΩ
430Ω
1%
150Ω
1%
1.1kΩ
68Ω
1%
FIGURE 1. PICOAMMETER CIRCUIT
Typical Performance Curves
1.0
0.8
TA = +25°C
RL = 100kΩ
0.6
0.4
0.2
VO-
0
-0.2
VO+
-0.4
VICR-
-0.6
VICR+
-0.8
-1.0
01
5
10
15
SUPPLY VOLTAGE (V)
FIGURE 3. OUTPUT VOLTAGE SWING AND COMMON MODE
INPUT VOLTAGE RANGE vs SUPPLY VOLTAGE
FIGURE 2. HIGH INPUT RESISTANCE VOLTMETER
10
TA = +25°C
V- = 0V
V+ = 2V
100 V+ = 5V
V+ = 10V
V+ = 20V
1000
0.001
0.1
1
10
LOAD (SOURCING) CURRENT (mA)
FIGURE 4. OUTPUT VOLTAGE vs LOAD SOURCING CURRENT
6
FN1925.6
December 8, 2009
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