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OPA349NA250G4 Datasheet(PDF) 9 Page - Texas Instruments |
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OPA349NA250G4 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 23 page OPA349, 2349 9 SBOS121B www.ti.com FIGURE 2. Simplified Schematic. FIGURE 1. AC-Coupled Amplifier. V BIAS1 V BIAS2 V IN+ V IN– Class AB Control Circuitry V O V– (Ground) V+ Reference Current APPLICATIONS INFORMATION The OPA349 series op amps are unity-gain stable and can operate on a single supply, making them highly versatile and easy to use. Power-supply pins should be bypassed with 0.01 µF ceramic capacitors. The OPA349 series op amps are fully specified and tested from +1.8V to +5.5V. Parameters that vary significantly with operating voltages or temperature are shown in the Typical Characteristic curves. The ultra-low quiescent current of the OPA349 requires careful application circuit techniques to achieve low overall current consumption. Figure 1 shows an ac-coupled amplifier biased with a voltage divider. Resistor values must be very large to minimize current. The large feedback resistor value reacts with input capacitance and stray capacitance to pro- duce a pole in the feedback network. A feedback capacitor may be required to assure stability and limit overshoot or gain peaking. Check circuit performance carefully to assure that biasing and feedback techniques meet signal and quies- cent current requirements. RAIL-TO-RAIL INPUT The input common-mode voltage range of the OPA349 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+) – 1.8V 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 degraded 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. V OUT OPA349 G = 11 C F 3pF +1.8V to 5.5V R 3 2M R 4 2M R 5 10M R 1 10M R 2 10M 10nF C F may be required for best stability or to reduce frequency peaking—see text. |
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