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OPA631U Datasheet(PDF) 11 Page - Burr-Brown (TI) |
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OPA631U Datasheet(HTML) 11 Page - Burr-Brown (TI) |
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11 / 17 page  11 ® OPA631, OPA632 APPLICATIONS INFORMATION WIDEBAND VOLTAGE-FEEDBACK OPERATION The OPA631 and OPA632 are unity-gain stable, very high- speed, voltage-feedback op amps designed for single-supply operation (+3V to +5V). The input stage supports input voltages below ground, and within 1.0V of the positive supply. The complementary common-emitter output stage provides an output swing to within 30mV of ground and 130mV of the positive supply. They are compensated to provide stable operation with a wide range of resistive loads. The OPA632’s internal disable circuitry is intended to mini- mize system power when disabled. Figure 1 shows the AC-coupled, gain of +2 configuration used for the +5V Specifications and Typical Performance Curves. For test purposes, the input impedance is set to 50 Ω with a resistor to ground. Voltage swings reported in the Specifications are taken directly at the input and output pins. For the circuit of Figure 1, the total effective load on the output at high frequencies is 150 Ω || 1500Ω. The disable pin (OPA635 only) needs to be driven by a low impedance source, such as a CMOS inverter. The 1.50k Ω resistors at the non-inverting input provide the common-mode bias voltage. Their parallel combination equals the DC resistance at the inverting input, minimizing the output DC offset. SINGLE-SUPPLY ADC CONVERTER INTERFACE The front page shows a DC-coupled, single-supply ADC driver circuit. Many systems are now requiring +3V supply capability of both the ADC and its driver. The OPA632 provides excellent performance in this demanding applica- tion. Its large input and output voltage ranges, and low distortion, support converters such as the ADS901 shown in this figure. The input level-shifting circuitry was designed so that VIN can be between 0V and 0.5V, while delivering an output voltage of 1V to 2V for the ADS901. Both the OPA632 and ADS901 have power reduction pins with the same polarity for those systems that need to conserve power. DC LEVEL SHIFTING Figure 3 shows a DC-coupled non-inverting amplifier that level-shifts the input up to accommodate the desired output voltage range. Given the desired signal gain (G), and the amount VOUT needs to be shifted up (∆VOUT) when VIN is at the center of its range, the following equations give the resistor values that produce the best DC offset. NG = G + ∆V OUT/VS R1 = R4/G R2 = R4/(NG – G) R3 = R4/(NG –1) where: NG = 1 + R4/R3 (Noise Gain) VOUT = (G)VIN + (NG – G)VS Make sure that VIN and VOUT stay within the specified input and output voltage ranges. Figure 2 shows the DC-coupled, gain of +2 configuration used for the +3V Specifications and Typical Performance Curves. For test purposes, the input impedance is set to 50 Ω with a resistor to ground. Though not strictly a “rail-to-rail” design, these parts come very close, while maintaining excellent performance. They will deliver ≈ 2.9Vp-p on a single +3V supply with 61MHz bandwidth. The 374 Ω and 2.26k Ω resistors at the input level-shift V IN so that VOUT is within the allowed output voltage range when VIN = 0. See the Typical Performance Curves for information on driving capacitive loads. FIGURE 1. AC-Coupled Signal—Resistive Load to Supply Midpoint. FIGURE 2. DC-Coupled Signal—Resistive Load to Supply Midpoint. OPA63x +V S = 5V DIS (OPA632 only) V OUT 53.6 Ω V IN 750 Ω 1.50k Ω 1.50k Ω R L 150 Ω +V S 2 750 Ω 6.8 µF + 0.1 µF 0.1 µF 0.1 µF + OPA63x +V S = 3V DIS (OPA632 only) V OUT 57.6 Ω V IN 562 Ω 374 Ω 2.26k Ω R L 150 Ω +V S 2 750 Ω 6.8 µF + 0.1 µF + |
Similar Part No. - OPA631U |
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Similar Description - OPA631U |
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