APPLICATIONS INFORMATION
OPA344 series op amps are unity gain stable and can operate
on a single supply, making them highly versatile and easy to
use. OPA345 series op amps are optimized for applications
requiring higher speeds with gains of 5 or greater.
Rail-to-rail input and output swing significantly increases
dynamic range, especially in low supply applications. Figure
1 shows the input and output waveforms for the OPA344 in
unity-gain configuration. Operation is from V
S
= +5V with
a 10kΩ load connected to V
S
/2. The input is a 5Vp-p
sinusoid. Output voltage is approximately 4.997Vp-p.
Power supply pins should be by passed with 0.01pF ceramic
capacitors.
OPERATING VOLTAGE
OPA344 and OPA345 series op amps are fully specified and
guaranteed from +2.7V to +5.5V. In addition, many specifi-
cations apply from –40ºC to +85ºC. Parameters that vary
significantly with operating voltages or temperature are
shown in the Typical Performance Curves.
RAIL-TO-RAIL INPUT
The input common-mode voltage range of the OPA344 and
OPA345 series extends 300mV beyond the supply rails.
This is achieved with a complementary input stage—an N-
channel input differential pair in parallel with a P-channel
differential pair (see Figure 2). The N-channel pair is active
for input voltages close to the positive rail, typically (V+) –
1.3V to 300mV above the positive supply, while the P-
channel pair is on for inputs from 300mV below the negative
supply to approximately (V+) –1.3V. There is a small
transition region, typically (V+) – 1.5V to (V+) – 1.1V, in
which both pairs are on. This 400mV transition region can
vary 300mV with process variation. Thus, the transition
region (both stages on) can range from (V+) – 1.8V to (V+)
– 1.4V on the low end, up to (V+) – 1.2V to (V+) – 0.8V on
the high end. Within the 400mV transition region PSRR,
CMRR, offset voltage, offset drift, and THD may be de-
graded compared to operation outside this region. For more
information on designing with rail-to-rail input op amps, see
Figure 3 “Design Optimization with Rail-to-Rail Input Op
Amps.”
Input
5V
G = +1, V
S
= +5V
0V
Output (inverted on scope)
5µs/div
FIGURE 1. Rail-to-Rail Input and Output.
1V/div
V+
Reference
Current
V
IN
+
V
IN
–
V
BIAS1
Class AB
Control
Circuitry
V
O
V
BIAS2
V–
(Ground)
FIGURE 2. Simplified Schematic.
9
OPA344, 2344, 4344
OPA345, 2345, 4345
®
BURR-BROWN [ BURR-BROWN CORPORATION ]
