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OPA349UA2K5G4 Datasheet(PDF) 10 Page - Texas Instruments |
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OPA349UA2K5G4 Datasheet(HTML) 10 Page - Texas Instruments |
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10 / 23 page  OPA349, 2349 10 SBOS121B www.ti.com R V IN V CM V OUT R FIGURE 3. Design Optimization. In most applications, operation is within the range of only one differential pair. However, some applications can subject the amplifier to a common-mode signal in the transition region. Under this condition, the inherent mismatch between the two differential pairs may lead to degradation of the CMRR and THD. The unity-gain buffer configuration is the most problem- atic—it will traverse through the transition region if a sufficiently DESIGN OPTIMIZATION WITH RAIL-TO-RAIL INPUT OP AMPS wide input swing is required. A design option would be to configure the op amp as a unity-gain inverter as shown below and hold the noninverting input at a set common-mode voltage outside the transition region. This can be accomplished with a voltage divider from the supply. The voltage divider should be designed such that the biasing point for the noninverting input is outside the transition region. COMMON-MODE REJECTION The CMRR for the OPA349 is specified in two ways so the best match for a given application may be used. First, the CMRR of the device in the common-mode range below the transition region (VCM < (V+) – 1.5V) is given. This specification is the best indicator of the capability of the device when the applica- tion requires use of one of the differential input pairs. Second, the CMRR at VS = 5V over the entire common-mode range is specified. OUTPUT DRIVEN TO V– RAIL Loads that connect to single-supply ground (or the V– supply pin) can cause the OPA349 or OPA2349 to oscillate if the output voltage is driven into the negative rail (as shown in Figure 4a). Similarly, loads that can cause current to flow out of the output pin when the output voltage is near V– can cause oscillations. The op amp will recover to normal opera- tion a few microseconds after the output is driven positively out of the rail. Some op amp applications can produce this condition even without a load connected to V–. The integrator in Figure 4b shows an example of this effect. Assume that the output ramps negatively, and saturates near 0V. Any negative- going step at VIN will produce a positive output current pulse through R1 and C1. This may incite the oscillation. Diode D1 prevents the input step from pulling output current when the output is saturated at the rail, thus preventing the oscillation. FIGURE 4. Output Driven to Negative Rail. V O V IN V+ OPA349 0V a) b) R L 1V (No Load) V IN V+ 2V 0V OPA349 0V C 1 1nF R 1 1M Ω D1 1N4148 |
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Similar Description - OPA349UA2K5G4 |
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