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OPA4343UA Datasheet(PDF) 9 Page - Texas Instruments |
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OPA4343UA Datasheet(HTML) 9 Page - Texas Instruments |
9 / 16 page OPA343, 2343, 4343 9 SBOS090A 5k Ω OPAx343 10mA max V+ V IN V OUT I OVERLOAD more than 500mV can cause excessive current to flow in or out of the input pins. Momentary voltages greater than 500mV beyond the power supply can be tolerated if the current on the input pins is limited to 10mA. This is easily accomplished with an input resistor, as shown in Figure 3. Many input signals are inherently current-limited to less than 10mA, therefore, a limiting resistor is not required. capacitive load reacts with the op amp’s output resistance, along with any additional load resistance, to create a pole in the small-signal response which degrades the phase margin. In unity gain, OPA343 series op amps perform well, with a pure capacitive load up to approximately 1000pF. Increasing gain enhances the amplifier’s ability to drive more capaci- tance. See the typical performance curve “Small-Signal Overshoot vs Capacitive Load.” One method of improving capacitive load drive in the unity gain configuration is to insert a 10 Ω to 20Ω resistor in series with the output, as shown in Figure 4. This significantly reduces ringing with large capacitive loads. However, if there is a resistive load in parallel with the capacitive load, RS creates a voltage divider. This introduces a dc error at the output and slightly reduces output swing. This error may be insignificant. For instance, with RL = 10kΩ and RS = 20Ω, there is only about a 0.2% error at the output. DRIVING A/D CONVERTERS OPA343 series op amps are optimized for driving medium speed (up to 100kHz) sampling A/D converters. However, they also offer excellent performance for higher-speed converters. The OPA343 series provides an effective means of buffering the A/D’s input capacitance and resulting charge injection while providing signal gain. For applica- tions requiring high accuracy, the OPA340 series is recom- mended. Figures 5 and 6 show the OPA343 driving an ADS7816. The ADS7816 is a 12-bit, micro-power sampling converter in the tiny MSOP-8 package. When used with the minia- ture package options of the OPA343 series, the combina- tion is ideal for space-limited and low-power applications. For further information consult the ADS7816 data sheet. With the OPA343 in a noninverting configuration, an RC network at the amplifier’s output can be used to filter high frequency noise in the signal (see Figure 5). In the invert- ing configuration, filtering may be accomplished with a capacitor across the feedback resistor (see Figure 6). FIGURE 3. Input Current Protection for Voltages Exceeding the Supply Voltage. RAIL-TO-RAIL OUTPUT A class AB output stage with common-source transistors is used to achieve rail-to-rail output. For light resistive loads (>50k Ω), the output voltage is typically a few millivolts from the supply rails. With moderate resistive loads (2k Ω to 50k Ω), the output can swing to within a few tens of milli- volts from the supply rails and maintain high open-loop gain. See the typical performanc curve “Output Voltage Swing vs Output Current.” CAPACITIVE LOAD AND STABILITY OPA343 series op amps can drive a wide range of capacitive loads. However, all op amps under certain conditions may become unstable. Op amp configuration, gain, and load value are just a few of the factors to consider when determin- ing stability. An op amp in unity gain configuration is the most susceptible to the effects of capacitive load. The FIGURE 4. Series Resistor in Unity-Gain Configuration Improves Capacitive Load Drive. 10 Ω to 20 Ω OPAx343 V+ V IN V OUT R S R L C L |
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