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OP271 Datasheet(PDF) 8 Page - Analog Devices |
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OP271 Datasheet(HTML) 8 Page - Analog Devices |
8 / 12 page REV. A OP271 –8– 1/2 OP271E A2 ASSUME: A1 AND A2 ARE MATCHED. AO(s) = s VO = (K1+1) VIN VIN V2 R2 R1 VO 1/2 OP271E A1 R2 K1 R2 = R1 R1 K1 OP271 R1 8.5V/ s PLACE SUPPLY DECOUPLING CAPACITORS AT OP271 VOUT CL 1000pF VIN V+ V– C2 10 F C3 0.1 F R2 R3 50 R1 + + C1 200pF C4 10 F C5 0.1 F OP271 Figure 2. Driving Large Capacitive Loads Figure 3. Pulsed Operation APPLICATION INFORMATION Capacitive Load Driving and Power Supply Considerations The OP217 is unity-gain stable and is capable of driving large capacitive loads without oscillating. Nonetheless, good supply bypassing is highly recommended. Proper supply bypassing reduces problems caused by supply line noise and improves the capacitive load driving capability of the OP271. In the standard feedback amplifier, the op amp’s output resistance combines with the load capacitance to form a low-pass filter that adds phase shift in the feedback network and reduces stability. A simple circuit to eliminate this effect is shown in Figure 2. The added components, C1 and R3, decouple the amplifier from the load capacitance and provide additional stability. The values of C1 and R3 shown in Figure 8 are for a load capacitance of up to 1000 pF when used with the OP271. Unity-Gain Buffer Applications When Rf 100 and the input is driven with a fast, large-signal pulse (>1 V), the output waveform will look as shown in Figure 3. During the fast feedthrough-like portion of the output, the input protection diodes effectively short the output to the input, and a current, limited only by the output short-circuit protection, will be drawn by the signal generator. With Rf 500 , the output is capable of handling the current requirements (IL 20 mA at 10 V); the amplifier will stay in its active mode and a smooth transition will occur. When Rf > 3 k , a pole created by Rf and the amplifier’s input capacitance (3 pF) creates additional phase shift and reduces phase margin. A small capacitor in parallel with Rf helps eliminate this problem. Computer Simulations Many electronic design and analysis programs include models for op amps which calculate AC performance from the location of poles and zeros. As an aid to designers utilizing such a program, major poles and zeros of the OP271 are listed below. Their location will vary slightly between production lots. Typically, they will be within 15% of the frequency listed. Use of this data will enable the designer to evaluate gross circuit performance quickly, but should not supplant rigorous characterization of a breadboard circuit. POLES ZEROS 15Hz 2.5 MHz 1.2 MHz 4 X 23 MHz 2 X 32 MHz - 8 X 40 MHz - APPLICATIONS Low Phase Error Amplifier The simple amplifier depicted in Figure 4, utilizes a monolithic dual operational amplifier and a few resistors to substantially reduce phase error compared to conventional amplifier designs. At a given gain, the frequency range for a specified phase accuracy is over a decade greater than for a standard single op amp amplifier. The low phase error amplifier performs second-order frequency compensation through the response of op amp A2 in the feedback loop of A1. Both op amps must be extremely well matched in frequency response. At low frequencies, the A1 feedback loop forces V2/(K1 + 1)=VIN. The A2 feedback loop forces VO/VIN=K1 + 1. The DC gain is determined by the resistor divider around A2. Note that, like a conventional single op amp amplifier, the DC gain is set by resistor ratios only. Minimum gain for the low phase error amplifier is 10. Figure 4. Low Phase Error Amplifier |
Similar Part No. - OP271_02 |
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Similar Description - OP271_02 |
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