OP295/OP495
Table I. Single Supply Low Noise P ream p P erform ance
unless this was a low distortion application such as audio. If this
is used to drive inductive loads, be sure to add diode clamps to
protect the bridge from inductive kickback.
IC = 1.85 m A
IC = 0.5 m A
R1
270 Ω
1.0 kΩ
D ir ect Access Ar r angem ent
R3, R4
200 Ω
910 Ω
OP295/OP495 can be used in a single supply Direct Access Ar-
rangement (DAA) as is shown an in Figure 4. T his figure shows
a portion of a typical DM capable of operating from a single
+5 volt supply and it may also work on +3 volt supplies with
minor modifications. Amplifiers A2 and A3 are configured so
that the transmit signal T XA is inverted by A2 and is not in-
verted by A3. T his arrangement drives the transformer differen-
tially so that the drive to the transformer is effectively doubled
over a single amplifier arrangement. T his application takes ad-
vantage of the OP295/OP495’s ability to drive capacitive loads,
and to save power in single supply applications.
en @ 100 Hz
en @ 10 Hz
ISY
3.15 nV/√Hz
4.2 nV/√Hz
4.0 mA
11 µA
1 kHz
1000
8.6 nV/√Hz
10.2 nV/√Hz
1.3 mA
3 µA
1 kHz
1000
IB
Bandwidth
Closed-Loop Gain
D r iving H eavy Loads
T he OP295/OP495 is well suited to drive loads by using a
power transistor, Darlington or FET to increase the current to
the load. T he ability to swing to either rail can assure that the
device is turned on hard. T his results in more power to the load
and an increase in efficiency over using standard op amps with
their limited output swing. Driving power FET s is also possible
with the OP295/OP495 because of its ability to drive capacitive
loads of several hundred picofarads without oscillating.
390pF
37.4kΩ
20kΩ
0.1µF
OP295/
OP495
A1
RXA
0.0047µF
Without the addition of external transistors the OP295/OP495
can drive loads in excess of ±15 mA with ±15 or +30 volt
supplies. T his drive capability is somewhat decreased at lower
supply voltages. At ±5 volt supplies the drive current is ±11 mA.
3.3kΩ
20kΩ
475Ω
OP295/
OP495
A2
22.1kΩ
Driving motors or actuators in two directions in a single supply
application is often accomplished using an “H” bridge. T he
principle is demonstrated in Figure 3a. From a single +5 volt
supply this driver is capable of driving loads from 0.8 V to 4.2 V
in both directions. Figure 3b shows the voltages at the inverting
and noninverting outputs of the driver. There is a small crossover
glitch that is frequency dependent and would not cause problems
0.1µF
20kΩ
750pF
TXA
1:1
0.033µF
20kΩ
20kΩ
OP295/
OP495
A3
2.5V REF
+5V
Figure 4. Direct Access Arrangem ent
2N2222
10k
2N2222
A Single Supply Instr um entation Am plifier
T he OP295/OP495 can be configured as a single supply instru-
OUTPUTS
0 ≤ V ≤ 2.5V
5k
IN
mentation amplifier as in Figure 5. For our example, VREF is set
V+
1.67V
10k
equal to
and VO is measured with respect to VREF. T he in-
2N2907
2
2N2907
10k
put common-mode voltage range includes ground and the out-
put swings to both rails.
V+
1/2
OP295/
5
6
8
4
OP495
1/2
VIN
7
Figure 3a. “H” Bridge
VO
OP295/
OP495
3
2
1
100
90
R1
R2
R4
100k
R3
20k
20k
100k
VREF
RG
200k
RG
V
IN + VREF
VO
= 5 +
(
)
10
0%
Figure 5. Single Supply Instrum entation Am plifier
2V
2V
1ms
Resistor RG sets the gain of the instrumentation amplifier. Mini-
mum gain is 6 (with no RG). All resistors should be matched in
absolute value as well as temperature coefficient to maximize
Figure 3b. “H” Bridge Outputs
–8–
REV. B
ADI [ ADI ]
