OPA445SM Datasheet, PDF (8/25 Pages) Texas Instruments – High Voltage FET-Input OPERATIONAL AMPLIFIER

OPA445
SBOS156B − MARCH 1987 − REVISED APRIL 2008
APPLICATIONS
Figure 1 shows the OPA445 connected as a basic
noninverting amplifier. The OPA445 can be used in
virtually any op amp configuration.
Power-supply terminals should be bypassed with 0.1µF
capacitors, or greater, near the power supply pins. Be sure
that the capacitors are appropriately rated for the
power-supply voltage used.
V+
0.1µF
R₁
G = 1+
R₂
R₁
R₂
OPA445
V_IN
0.1µF
V−
V_O
Z_L
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INPUT PROTECTION
The inputs of conventional FET-input op amps should be
protected against destructive currents that can flow when
input FET gate-to-substrate isolation diodes are
forward-biased. This can occur if the input voltage
exceeds the power supplies or there is an input voltage
with V_S = 0V. Protection is easily accomplished with a
resistor in series with the input. Care should be taken
because the resistance in series with the input
capacitance may affect stability. Many input signals are
inherently current-limited; therefore, a limiting resistor may
not be required.
OFFSET VOLTAGE TRIM
The OPA445 provides offset voltage trim connections on
pins 1 and 5. Offset voltage can be adjusted by connecting
a potentiometer as shown in Figure 2. This adjustment
should be used only to null the offset of the op amp, not to
adjust system offset or offset produced by the signal
source. Nulling system offset could degrade the offset
voltage drift behavior of the op amp. While it is not possible
to predict the exact change in drift, the effect is usually
small.
Figure 1. The OPA445 Configured as a
Noninverting Amplifier
POWER SUPPLIES
The OPA445 may be operated from power supplies up to
±45V or a total of 90V with excellent performance. Most
behavior remains unchanged throughout the full operating
voltage range. Parameters which vary significantly with
operating voltage are shown in the Typical Characteristics.
Some applications do not require equal positive and
negative output voltage swing. Power-supply voltages do
not need to be equal. The OPA445 can operate with as little
as 20V between the supplies and with up to 90V between
the supplies. For example, the positive supply could be set
to 80V with the negative supply at −10V, or vice-versa.
V+
7
2
Use offset adjust pins
only to null offset voltage
of op amp−see text.
OPA445 ⁶
3
1 _{10mV Typical}
5
Trim Range
4
(1)
NOTE: (1) 10kΩ to 1MΩ
Trim Potentiometer
V−
(100kΩ recommended).
Figure 2. Offset Voltage Trim
8