OPA347NA Datasheet, PDF (7/33 Pages) Texas Instruments – microPower, Rail-to-Rail Operational Amplifiers

APPLICATIONS INFORMATION
The OPA347 series op amps are unity-gain stable and can
operate on a single supply, making them highly versatile and
easy to use.
Rail-to-rail input and output swing significantly increases dy-
namic range, especially in low supply applications. Figure 1
shows the input and output waveforms for the OPA347 in
unity-gain configuration. Operation is from V_S = +5V with a
100kΩ load connected to V_S/2. The input is a 5V_PP sinusoid.
Output voltage is approximately 4.995V_PP.
Power-supply pins should be bypassed with 0.01µF ceramic
capacitors.
5V
1V/div
Input
G = +1, V_S = +5V
0V
Output (inverted on scope)
20µs/div
OPERATING VOLTAGE
The OPA347 series op amps are fully specified and en-
sured from 2.5V to 5.5V. In addition, many specifications
apply from –55°C to +125°C. Parameters that vary signifi-
cantly with operating voltages or temperature are shown in
the Typical Characteristics.
RAIL-TO-RAIL INPUT
The input common-mode voltage range of the OPA347
series extends 200mV 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, as shown in Figure 2. The N-channel pair is active for
input voltages close to the positive rail, typically (V+) – 1.3V
to 200mV above the positive supply, while the P-channel pair
is on for inputs from 200mV 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+) – 1.65V to (V+) – 1.25V on the low
end, up to (V+) – 1.35V to (V+) – 0.95V on the high end.
Within the 400mV transition region PSRR, CMRR, offset
voltage, and offset drift may be degraded compared to
operation outside this region. For more information on de-
signing with rail-to-rail input op amps, see Figure 3, Design
Optimization with Rail-to-Rail Input Op Amps.
FIGURE 1. Rail-to-Rail Input and Output.
V+
V_IN+
Reference
Current
V_IN–
V_BIAS1
Class AB
Control
V_O
Circuitry
V_BIAS2
V–
(Ground)
FIGURE 2. Simplified Schematic.
OPA347, 2347, 4347
7
SBOS167D
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