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CA3420EZ Datasheet PDF : 5 Pages
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CA3420
Electrical Specifications For Equipment Design, at VSUPPLY = ±10V, TA = 25°C, Unless Otherwise Specified
TEST
PARAMETER
SYMBOL CONDITIONS
MIN
TYP
MAX
UNITS
Input Offset Voltage
Input Offset Current (Note 4)
Input Current (Note 4)
Large Signal Voltage Gain
|VIO|
|IIO|
|II|
AOL
RL = 10kΩ
-
5
10
mV
-
0.03
4
pA
-
0.05
5
pA
10
100
-
kV/V
80
100
-
dB
Common Mode Rejection Ratio
CMRR
-
100
320
µV/V
70
80
-
dB
Common Mode Input Voltage Range
Power Supply Rejection Ratio
Max Output Voltage
Supply Current
VlCR+
VlCR-
PSRR
∆VIO/∆V
VOM+
VOM-
I+
RL = ∞
8.5
9.3
-
V
-10
-10.3
-
V
-
32
320
µV/V
70
90
-
dB
9.7
9.9
-
V
-9.7
-9.85
-
V
-
450
1000
µA
Device Dissipation
Input Offset Voltage Temperature Drift
NOTE:
PD
∆VlO/∆T
-
9
14
mW
-
4
-
µV/°C
4. The maximum limit represents the levels obtainable on high speed automatic test equipment. Typical values are obtained under laboratory conditions.
Typical Applications
Picoammeter Circuit
The exceptionally low input current (typically 0.2pA) makes
the CA3420 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
CA3420 decouples the potentially high input capacitance
often associated with lower current circuits and reduces the
tendency for the circuit to oscillate under these conditions.
High Input Resistance Voltmeter
Advantage is taken of the high input impedance of the CA3420
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 coefficient 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.
1MΩ
10GΩ
10MΩ
10pF
+1.5V
2-
7
500-0-500
µA
CA3420
6
M
3+
4
±50pA
5
1
BATTERY
RETURNS ±15pA
10kΩ
1.5kΩ
1.5kΩ, 1%
1kΩ
±5pA
430Ω, 1%
-1.5V
±1.5pA 150Ω, 1%
11kΩ
68Ω
1%
FIGURE 1. PICOAMMETER CIRCUIT
22MΩ
+1.5V
3
10MΩ
+
7
CA3420 6
500-0-500
µA
M
100pF
2
-
4
±500mV
5
1
BATTERY
RETURNS
10kΩ
±150mV
1.5kΩ
1.5kΩ, 1%
1kΩ
-1.5V
430Ω, 1%
±50mV
150Ω, 1%
±15mV
1.1kΩ
68Ω
1%
FIGURE 2. HIGH INPUT RESISTANCE VOLTMETER
3
FN1320.9
October 4, 2005
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