OP295/OP495
Table I. Single Supply Low Noise Preamp Performance
I
C
= 1.85 mA
R1
R3, R4
e
n
@ 100 Hz
e
n
@ 10 Hz
I
SY
I
B
Bandwidth
Closed-Loop Gain
Driving Heavy Loads
I
C
= 0.5 mA
1.0 kΩ
910
Ω
8.6 nV/√Hz
10.2 nV/√Hz
1.3 mA
3
µA
1 kHz
1000
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.
Direct Access Arrangement
270
Ω
200
Ω
3.15 nV/√Hz
4.2 nV/√Hz
4.0 mA
11
µA
1 kHz
1000
The OP295/OP495 is 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 its ability to drive capacitive
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 or +30 volt
supplies. This drive capability is somewhat decreased at lower
supply voltages. At
±
5 volt 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 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
+5V
2N2222
10k
0
≤
V
IN
≤
2.5V 5k
1.67V
10k
10k 2N2907
2N2907
OUTPUTS
OP295/OP495 can be used in a single supply Direct Access Ar-
rangement (DAA) as is shown an in Figure 4. This 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 TXA is inverted by A2 and is not in-
verted by A3. This arrangement drives the transformer differen-
tially so that the drive to the transformer is effectively doubled
over a single amplifier arrangement. This application takes ad-
vantage of the OP295/OP495’s ability to drive capacitive loads,
and to save power in single supply applications.
390pF
37.4kΩ
20kΩ
0.1µF
RXA
0.0047µF
3.3kΩ
20kΩ
475Ω
A2
22.1kΩ
0.1µF
TXA
20kΩ
20kΩ
0.033µF
20kΩ
750pF
1:1
A1
OP295/
OP495
OP295/
OP495
2.5V REF
OP295/
OP495
A3
2N2222
Figure 4. Direct Access Arrangement
A Single Supply Instrumentation Amplifier
The OP295/OP495 can be configured as a single supply instru-
mentation amplifier as in Figure 5. For our example, V
REF
is set
V
+
equal to
and V
O
is measured with respect to V
REF
. The in-
2
put common-mode voltage range includes ground and the out-
put swings to both rails.
V+
Figure 3a. “H” Bridge
V
IN
3
1/2
OP295/
OP495
1
5
8
1/2
OP295/
OP495
7
V
O
6
4
2
100
90
R1
100k
V
REF
R2
20k
R
G
V
O
= 5 +
R3
20k
R4
100k
(
200k
R
G
)
V
IN
+ V
REF
10
0%
Figure 5. Single Supply Instrumentation Amplifier
2V
2V
1ms
Figure 3b. “H” Bridge Outputs
Resistor R
G
sets the gain of the instrumentation amplifier. Mini-
mum gain is 6 (with no R
G
). All resistors should be matched in
absolute value as well as temperature coefficient to maximize
–8–
REV. B
AD [ ANALOG DEVICES ]
