ca5420a Intersil Corporation, ca5420a Datasheet - Page 5

• Manufacturer Part Number: ca5420a
• Description: 0.5mhz, Low Supply Voltage, Low Input Current Bimos Operational Amplifiers
• Manufacturer: Intersil Corporation

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.
Typical Performance Curves
FIGURE 3. OUTPUT VOLTAGE SWING AND COMMON MODE
1MΩ
-0.2
-0.4
-0.6
-0.8
-1.0
1.0
0.8
0.6
0.4
0.2
0
0
10GΩ
10MΩ
T
R
INPUT VOLTAGE RANGE vs SUPPLY VOLTAGE
A
L
FIGURE 1. PICOAMMETER CIRCUIT
1
= 25°C
= 100kΩ
10kΩ
2
3
10pF
CA5420A
+
1
-
SUPPLY VOLTAGE (V)
5
5
+1.5V
5
4
7
-1.5V
RETURNS
BATTERY
6
10
500-0-500
±15pA
±1.5pA
±50pA
±5pA
µA
V
V
V
V
M
11kΩ
O
O
ICR
ICR
-
+
-
+
68Ω
1%
1.5kΩ
1%
430Ω
1%
150Ω
1%
1.5kΩ
1kΩ
15
CA5420A
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 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.
FIGURE 4. OUTPUT VOLTAGE vs LOAD SOURCING CURRENT
22MΩ
FIGURE 2. HIGH INPUT RESISTANCE VOLTMETER
1000
100
10
0.001
V+ = 2V
V+ = 5V
V+ = 10V
V+ = 20V
T
V- = 0V
A
10MΩ
100pF
= 25°C
10kΩ
3
2
LOAD (SOURCING) CURRENT (mA)
CA5420A
+
1
-
0.1
5
+1.5V
4
7
BATTERY
RETURNS
-1.5V
6
500-0-500
±500mV
±150mV
±15mV
±50mV
µA
1
1.1kΩ
M
December 21, 2005
150Ω
1%
68Ω
1%
1.5kΩ
1%
430Ω
1%
1.5kΩ
1kΩ
FN1925.5
10