OP295_06 Datasheet, PDF (10/16 Pages) Analog Devices – Dual/Quad Rail-to-Rail Operational Amplifiers

OP295/OP495
Finally, the potentiometer, R8, is needed to adjust the offset
voltage to null it to zero. Similar performance can be obtained
using an OP90 as the output amplifier with a savings of about
185 μA of supply current. However, the output swing does not
include the positive rail, and the bandwidth reduces to approxi-
mately 250 Hz.
Table 6. Single-Supply Low Noise Preamp Performance
IC = 1.85 mA
IC = 0.5 mA
R1
270 Ω
1.0 kΩ
R3, R4
en @ 100 Hz
en @ 10 Hz
ISY
IB
Bandwidth
Closed-Loop Gain
200 Ω
3.15 nV/√Hz
4.2 nV/√Hz
4.0 mA
11 μA
1 kHz
1000
910 Ω
8.6 nV/√Hz
10.2 nV/√Hz
1.3 mA
3 μA
1 kHz
1000
DRIVING HEAVY LOADS
The OP295/OP495 are well suited to drive loads by using a
power transistor, Darlington, or FET to increase the current to
the load. The ability to swing to either rail can assure that the
device is turned on hard. This results in more power to the load
and an increase in efficiency over using standard op amps with
their limited output swing. Driving power FETs is also possible
with the OP295/OP495 because of their ability to drive capaci-
tive loads of several hundred picofarads without oscillating.
Without the addition of external transistors, the OP295/OP495
can drive loads in excess of ±15 mA with ±15 V or +30 V
supplies. This drive capability is somewhat decreased at lower
supply voltages. At ±5 V supplies, the drive current is ±11 mA.
Driving motors or actuators in two directions in a single-supply
application is often accomplished using an H bridge. The
principle is demonstrated in Figure 20. From a single 5 V
supply, this driver is capable of driving loads from 0.8 V to
4.2 V in both directions. Figure 21 shows the voltages at the
inverting and noninverting outputs of the driver. There is a
small crossover glitch that is frequency-dependent; it does not
cause problems unless used in low distortion applications, such
as audio. If this is used to drive inductive loads, diode clamps
should be added to protect the bridge from inductive kickback.
5V
0 ≤ V_IN ≤ 2.5V _5kΩ
1.67V
2N2222
10kΩ
–
+
10kΩ 10kΩ ^2N2907
2N2222
OUTPUTS
2N2907
–
+
Figure 20. H Bridge
100
90
10
0%
2V
2V
1ms
Figure 21. H Bridge Outputs
DIRECT ACCESS ARRANGEMENT
The OP295/OP495 can be used in a single-supply direct access
arrangement (DAA), as shown in Figure 22. This figure shows
a portion of a typical DM capable of operating from a single 5 V
supply, and it may also work on 3 V supplies with minor modi-
fications. Amplifier A2 and Amplifier A3 are configured so that
the transmit signal, TxA, is inverted by A2 and is not inverted
by A3. This arrangement drives the transformer differentially so
the drive to the transformer is effectively doubled over a single
amplifier arrangement. This application takes advantage of the
ability of the OP295/OP495 to drive capacitive loads and to save
power in single-supply applications.
390pF
0.1µF
RxA
37.4kΩ
–
A1
+
0.0047µF
OP295/
OP495 20kΩ
3.3kΩ
20kΩ
OP295/ A2
475Ω
OP495
0.1µF
TxA
22.1kΩ
20kΩ ^750pF
20kΩ
0.033µF
1:1
20kΩ
2.5V REF
OP295/
OP495 ^A3
Figure 22. Direct Access Arrangement
SINGLE-SUPPLY INSTRUMENTATION AMPLIFIER
The OP295/OP495 can be configured as a single-supply
instrumentation amplifier, as shown in Figure 23. For this
example, VREF is set equal to V+/2, and VO is measured with
respect to VREF. The input common-mode voltage range
includes ground, and the output swings to both rails.
Rev. E | Page 10 of 16