OPA354A-Q1 Datasheet, PDF (13/37 Pages) Texas Instruments – 250-MHz, Rail-to-Rail I/O, CMOS Operational Amplifiers

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OPA354A-Q1, OPA2354A-Q1, OPA4354-Q1
SBOS492E – JUNE 2009 – REVISED AUGUST 2016
Feature Description (continued)
7.3.2 Rail-to-Rail Input
The specified input common-mode voltage range of the OPAx354-Q1 family of devices extends 100 mV beyond
the supply rails. A complementary input stage—an N-channel input differential pair in parallel with a P-channel
differential pair—achieves this extension. The N-channel pair is active for input voltages close to the positive rail,
typically (V+) – 1.2 V to 100 mV above the positive supply, while the P-channel pair is on for inputs from 100 mV
below the negative supply to approximately (V+) – 1.2 V. A small transition region exists, typically (V+) – 1.5 V to
(V+) – 0.9 V, in which both pairs are on. This 600-mV transition region can vary ±500 mV with process variation.
Thus, the transition region (both input stages on) can range from (V+) – 2 V to (V+) – 1.5 V on the low end, up to
(V+) – 0.9 V to (V+) – 0.4 V on the high end.
A double-folded cascode adds the signal from the two input pairs and presents a differential signal to the class
AB output stage.
7.3.3 Rail-to-Rail Output
The device uses a class-AB output stage with common-source transistors to achieve rail-to-rail output. For high-
impedance loads (> 200 Ω), the output voltage swing is typically 100 mV from the supply rails. With 10-Ω loads,
one can achieve a useful output swing while maintaining high open-loop gain. See Figure 20, Output Voltage
Swing vs Output Current.
7.3.4 Output Drive
The OPAx354-Q1 output stage can supply a continuous output current of ±100 mA and still provide
approximately 2.7-V output swing on a 5-V supply, as shown in Figure 30.
R₂
1kW
C₁
50pF
+
V₁
- ^5V
R₁
10kW
1mF
V+
OPA354-Q1
R₃
V_IN ^10kW
+
-
1V In = 100mA
Out, as Shown
V-
R₄
1kW
R_SHUNT
1W
Laser Diode
Figure 30. Laser Diode Driver
For maximum reliability, TI does not recommend running a continuous dc current in excess of ±100 mA. See
Figure 20, Output Voltage Swing vs Output Current. A solution for supplying continuous output currents greater
than ±100 mA is operating OPAx354-Q1 family of devices in parallel, as shown in Figure 31.
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