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OPA2690I-14D Datasheet(PDF) 13 Page - Burr-Brown (TI) |
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OPA2690I-14D Datasheet(HTML) 13 Page - Burr-Brown (TI) |
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13 / 30 page  OPA2690 SBOS238D − JUNE 2002 − REVISED DECEMBER 2004 www.ti.com 13 APPLICATIONS INFORMATION WIDEBAND VOLTAGE-FEEDBACK OPERATION The OPA2690 provides an exceptional combination of high output power capability in a dual, wideband, unity-gain stable, voltage-feedback op amp using a new high slew rate input stage. Typical differential input stages used for voltage-feedback op amps are designed to steer a fixed-bias current to the compensation capacitor, setting a limit to the achievable slew rate. The OPA2690 uses a new input stage which places the transconductance element between two input buffers, using their output currents as the forward signal. As the error voltage increases across the two inputs, an increasing current is delivered to the compensation capacitor. This provides very high slew rate (1800V/ µs) while consuming relatively low quiescent current (5.5mA/ch). This exceptional full-power performance comes at the price of a slightly higher input noise voltage than alternative architectures. The 5.5nV/ √Hz input voltage noise for the OPA2690 is exceptionally low for this type of input stage. Figure 1 shows the DC-coupled, gain of +2, dual power- supply circuit configuration used as the basis of the ±5V Electrical Characteristics and Typical Characteristics. This is for one channel; the other channel is connected similarly. For test purposes, the input impedance is set to 50 Ω with a resistor to ground and the output impedance is set to 50 Ω with a series output resistor. Voltage swings reported in the electrical characteristics are taken directly at the input and output pins, while output powers (dBm) are at the matched 50 Ω load. For the circuit of Figure 1, the total effective load will be 100 Ω 804Ω. The disable control line (SO-14 package only) is typically left open for normal amplifier operation. Two optional components are included in Figure 1. An additional resistor (175 Ω) is included in series with the noninverting input. Combined with the 25 Ω DC source resistance looking back towards the signal generator, this gives an input bias current cancelling resistance that matches the 200 Ω source resistance seen at the inverting input (see the DC Accuracy and Offset Control section). In addition to the usual power-supply decoupling capacitors to ground, a 0.1 µF capacitor is included between the two power-supply pins. In practical PC board layouts, this optional-added capacitor will typically improve the 2nd-harmonic distortion performance by 3dB to 6dB. Figure 2 shows the AC-coupled, gain of +2, single-supply circuit configuration used as the basis of the +5V Electrical and Typical Characteristics. Though not a rail-to-rail design, the OPA2690 requires minimal input and output voltage headroom compared to other very wideband voltage-feedback op amps. It will deliver a 3VPP output swing on a single +5V supply with > 150MHz bandwidth. The key requirement of broadband single-supply operation is to maintain input and output signal swings within the useable voltage ranges at both the input and the output. The circuit of Figure 2 establishes an input midpoint bias using a simple resistive divider from the +5V supply (two 698 Ω resistors). Separate bias networks would be required at each input. The input signal is then AC-coupled into the midpoint voltage bias. The input voltage can swing to within 1.5V of either supply pin, giving a 2VPP input signal range centered between the supply pins. The input impedance matching resistor (59 Ω) used for testing is adjusted to give a 50 Ω input load when the parallel combination of the biasing divider network is included. 1/2 OPA2690 +5V +V S −V S + DIS −5V 50 ΩLoad 50 Ω 175 Ω 50 Ω V O V D V I 50 ΩSource R G 402 Ω R F 402 Ω 6.8 µF 0.1 µF6.8µF 0.1 µF 0.1 µF Figure 1. DC-Coupled, G = +2, Bipolar Supply, Specification and Test Circuit 1/2 OPA2690 +5V +V S DIS V S/2 698 Ω 100 Ω V O V D V I 698 Ω 50 Ω R G 402 Ω R F 402 Ω 0.1 µF 0.1 µF 59 Ω 6.8 µF 0.1 µF Figure 2. DC-Coupled, G = +2, Single-Supply, Specification and Test Circuit |
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