OPA348-Q1 Datasheet, PDF (10/30 Pages) Texas Instruments – OPAx348-Q1 1-MHz 45-μA CMOS Rail-to-Rail Operational Amplifier

OPA348-Q1, OPA2348-Q1, OPA4348-Q1
SBOS465B – JANUARY 2009 – REVISED DECEMBER 2014
7.3 Feature Description
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7.3.1 Operating Voltage
The OPAx348-Q1 op-amp is fully specified and ensured for operation from 1.8 V to 5.5 V. In addition, many
specifications apply from –40°C to 125°C. Parameters that vary significantly with operating voltages or
temperature are shown in the Typical Characteristics graphs. Power-supply pins should be bypassed with 0.01-
μF ceramic capacitors.
7.3.2 Rail-to-Rail Input
The input common-mode voltage range of the OPAx348-Q1 family of devices extends 200 mV beyond the supply
rails. This performance is achieved with a complementary input stage: an N-channel input differential pair in
parallel with a P-channel differential pair. The N-channel pair is active for input voltages close to the positive rail,
typically (V+) – 1.3 V to 200 mV above the positive supply. The P-channel pair is on for inputs from 200 mV
below the negative supply to approximately (V+) – 1.3 V. A small transition region exists, typically (V+) – 1.4 V to
(V+) – 1.2 V, in which both pairs are on. This 200-mV transition region can vary up to 300 mV with process
variation. Thus, the transition region (both stages on) can range from (V+) – 1.7 V to (V+) – 1.5 V on the low end,
up to (V+) – 1.1 V to (V+) – 0.9 V on the high end. Within this transition region, PSRR, CMRR, offset voltage,
offset drift, and THD may be degraded compared to device operation outside this region.
7.3.3 Rail-to-Rail Input
The input common-mode range extends from (V–) – 0.2 V to (V+) + 0.2 V. For normal operation, the inputs
should be limited to this range. The absolute maximum input voltage is 500 mV beyond the supplies. Inputs
greater than the input common-mode range but less than the maximum input voltage, while not valid, do not
cause any damage to the op-amp. Unlike some other op-amps, if the input current is limited the inputs may go
beyond the power supplies without phase inversion, as shown in Figure 19.
V_IN
G = +1V/V, V _S = +5V
5V
V_OUT
0V
10µs/div
Figure 19. No-Phase Inversion With Inputs Greater Than Power-Supply Voltage
Normally, input currents are 0.5 pA. However, large inputs (greater than 500 mV beyond the supply rails) can
cause excessive current to flow in or out of the input pins. Therefore, limiting the input current to less than 10 mA
is important as well as keeping the input voltage below the maximum rating. This limiting is easily accomplished
with an input voltage resistor, as shown in Figure 20.
I_OVERLOAD
10mA max
V_IN
5kW
+5V
1/2
OPA2348
V_OUT
Figure 20. Input Current Protection for Voltages Exceeding the Supply Voltage
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