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OPA4345UAG4 Datasheet(PDF) 11 Page - Texas Instruments |
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OPA4345UAG4 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 28 page www.ti.com SBOS107A OPA344, 2344, 4344 OPA345, 2345, 4345 11 performance curve “Small-Signal Overshoot vs Capacitive Load.” In unity-gain configurations, capacitive load drive can be improved by inserting a small (10 Ω to 20Ω) resistor, RS, in series with the output, as shown in Figure 5. This significantly reduces ringing while maintaining dc perfor- mance for purely capacitive loads. However, if there is a resistive load in parallel with the capacitive load, a voltage divider is created, introducing a dc error at the output and slightly reducing the output swing. The error introduced is proportional to the ratio RS/RL, and is generally negligible. FIGURE 6. OPA344 in Noninverting Configuration Driving ADS7822. FIGURE 7. Speech Bandpass Filtered Data Acquisition System. DRIVING A/D CONVERTERS The OPA344 and OPA345 series op amps are optimized for driving medium-speed sampling A/D converters. The OPA344 and OPA345 op amps buffer the A/D’s input capacitance and resulting charge injection while providing signal gain. Figures 6 shows the OPA344 in a basic noninverting con- figuration driving the ADS7822. The ADS7822 is a 12-bit, micro-power sampling converter in the MSOP-8 package. When used with the low-power, miniature packages of the OPA344, the combination is ideal for space-limited, low- power applications. In this configuration, an RC network at the A/D’s input can be used to filter charge injection. Figure 7 shows the OPA2344 driving an ADS7822 in a speech bandpass filtered data acquisition system. This small, low-cost solution provides the necessary amplification and signal conditioning to interface directly with an electret microphone. This circuit will operate with VS = +2.7V to +5V with less than 500 µA quiescent current. FIGURE 5. Series Resistor in Unity-Gain Configuration Improves Capacitive Load Drive. 10 Ω to 20 Ω OPA344 V+ V IN V OUT R S R L C L C 3 33pF V+ GND 3 1 8 4 5 6 7 –IN +IN 2 C 2 DCLOCK Serial Interface 1000pF R 1 1.5k Ω R 4 20k Ω R 5 20k Ω R 6 100k Ω R 8 150k Ω R 9 510k Ω R 7 51k Ω D OUT V REF V+ = +2.7V to 5V CS/SHDN C1 1000pF Electret Microphone(1) G = 100 Passband 300Hz to 3kHz R 3 1M Ω R 2 1M Ω NOTE: (1) Electret microphone powered by R 1. ADS7822 12-Bit A/D 1/2 OPA2344 1/2 OPA2344 ADS7822 12-Bit A/D DCLOCK D OUT CS/SHDN OPA344 +5V V IN V+ 2 +In 3 –In V REF 8 4 GND Serial Interface 1 0.1 µF 0.1 µF 7 6 5 NOTE: A/D Input = 0 to V REF V IN = 0V to 5V for 0V to 5V output. RC network filters high frequency noise. 500 Ω 3300pF |
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