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AD8542ARZ Folha de dados(PDF) 9 Page - Analog Devices |
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AD8542ARZ Folha de dados(HTML) 9 Page - Analog Devices |
9 / 16 page AD8541/AD8542/AD8544 –9– REV. D FREQUENCY – kHz 05 25 10 15 20 VS = 5V AV = 1 MARKER SET @ 10kHz MARKER READING: 37.6 V/ Hz TA = 25 C TPC 30. Voltage Noise FREQUENCY – Hz 1k 10k 100M 100k 1M 10M 1,000 900 0 800 700 600 500 400 300 200 100 VS = 2.7V AND 5V AV = 1 TA = 25 C TPC 29. Closed-Loop Output Impedance vs. Frequency NOTES ON THE AD854x AMPLIFIERS The AD8541/AD8542/AD8544 amplifiers are improved perfor- mance general-purpose operational amplifiers. Performance has been improved over previous amplifiers in several ways. Lower Supply Current for 1 MHz Gain Bandwidth The AD854x series typically uses 45 mA of current per amplifier. This is much less than the 200 mA to 700 mA used in earlier generation parts with similar performance. This makes the AD854x series a good choice for upgrading portable designs for longer battery life. Alternatively, additional functions and per- formance can be added at the same current drain. Higher Output Current At 5 V single supply, the short-circuit current is typically 60 mA. Even 1 V from the supply rail, the AD854x amplifiers can provide 30 mA, sourcing or sinking. Sourcing and sinking are strong at lower voltages, with 15 mA available at 2.7 V and 18 mA at 3.0 V. For even higher output currents, please see the Analog Devices AD8531/AD8532/AD8534 parts, with output currents to 250 mA. Information on these parts is available from your Analog Devices representative, and data sheets are available at the Analog Devices website at www.analog.com. Better Performance at Lower Voltages The AD854x family of parts has been designed to provide better ac performance, at 3.0 V and 2.7 V, than previously available parts. Typical gain-bandwidth product is close to 1 MHz at 2.7 V. Voltage gain at 2.7 V and 3.0 V is typically 500,000. Phase margin is typically over 60 ∞C, making the part easy to use. APPLICATIONS Notch Filter The AD8542 has very high open-loop gain (especially with a supply voltage below 4 V), which makes it useful for active filters of all types. For example, Figure 1 illustrates the AD8542 in the classic Twin-T Notch Filter design. The Twin-T Notch is desired for simplicity, low output impedance, and minimal use of op amps. In fact, this notch filter may be designed with only one op amp if Q adjustment is not required. Simply remove U2 as illus- trated in Figure 2. However, a major drawback to this circuit topology is ensuring that all the Rs and Cs closely match. The components must closely match or notch frequency offset and drift will cause the circuit to no longer attenuate at the ideal notch frequency. To achieve desired performance, 1% or better component tolerances or special component screens are usually required. One method to desensitize the circuit- to-component mismatch is to increase R2 with respect to R1, which lowers Q. A lower Q increases attenuation over a wider frequency range but reduces attenuation at the peak notch frequency. 1/2 AD8542 [ ] 4 1 R1 R1+R2 1 2 pRC C 26.7nF R1 97.5k C2 53.6 F R/2 50k R2 2.5k R 100k R 100k 5 6 7 8 3 2 VOUT 4 1 1/2 AD8542 5.0V 2.5VREF C 26.7nF 2.5VREF f0 = 1 f0 = U2 U1 Figure 1. 60 Hz Twin-T Notch Filter, Q = 10 C 2C R/2 R R 7 3 2 VOUT 4 6 AD8541 5.0V 2.5VREF C VIN Figure 2. 60 Hz Twin-T Notch Filter, Q = • (Ideal) Figure 3 shows another example of the AD8542 in a notch filter circuit. The FNDR notch filter has fewer critical matching requirements than the Twin-T Notch and for the FNDR Q is directly proportional to a single resistor R1. While matching component values is still important, it is also TEMPERATURE – C 55 20 55 35 145 15 525 45 65 85 105 125 50 45 40 35 30 25 VS = 5V VS = 2.7V TPC 28. Supply Current per Amplifier vs. Temperature |
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