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OPA1632 Datasheet(PDF) 7 Page - Burr-Brown (TI) |
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OPA1632 Datasheet(HTML) 7 Page - Burr-Brown (TI) |
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7 / 16 page  OPA1632 SBOS286A − DECEMBER 2003 − REVISED SEPTEMBER 2006 www.ti.com 7 FULLY-DIFFERENTIAL AMPLIFIERS Differential signal processing offers a number of performance advantages in high-speed analog signal processing systems, including immunity to external common-mode noise, suppression of even-order nonlinearities, and increased dynamic range. Fully-dif- ferential amplifiers not only serve as the primary means of providing gain to a differential signal chain, but also provide a monolithic solution for converting single-en- ded signals into differential signals allowing for easy, high-performance processing. A standard configuration for the device is shown in Figure 2. The functionality of a fully differential amplifier can be imagined as two inverting amplifiers that share a common noninverting terminal (though the voltage is not necessarily fixed). For more information on the basic theory of operation for fully differential amplifiers, refer to the Texas Instruments application note SLOA054, Fully Differential Amplifiers, available for download from the TI web site (www.ti.com). +15V Digital Output −15V V OCM V REF V IN+ V IN − A IN A IN Figure 2. Typical ADC Circuit SHUTDOWN FUNCTION The shutdown (enable) function of the OPA1632 is referenced to the negative supply of the operational amplifier. A valid logic low (< 0.8V above negative supply) applied to the enable pin (pin 7) disables the amplifier output. Voltages applied to pin 7 that are greater than 2V above the negative supply place the amplifier output in an active state, and the device is enabled. If pin 7 is left disconnected, an internal pull-up resistor enables the device. Turn-on and turn-off times are approximately 2 µs each. Quiescent current is reduced to approximately 0.85mA when the amplifier is disabled. When disabled, the output stage is not in a high-impedance state. Thus, the shutdown function cannot be used to create a multiplexed switching function in series with multiple amplifiers. OUTPUT COMMON-MODE VOLTAGE The output common-mode voltage pin sets the DC output voltage of the OPA1632. A voltage applied to the VOCM pin from a low-impedance source can be used to directly set the output common-mode voltage. For a VOCM voltage at mid-supply, make no connection to the VOCM pin. Depending on the intended application, a decoupling capacitor is recommended on the VOCM node to filter any high-frequency noise that could couple into the signal path through the VOCM circuitry. A 0.1µF or 1µF capacitor is generally adequate. Output common-mode voltage causes additional current to flow in the feedback resistor network. Since this current is supplied by the output stage of the amplifier, this creates additional power dissipation. For commonly-used feedback resistance values, this current is easily supplied by the amplifier. The additional internal power dissipation created by this current may be significant in some applications and may dictate use of the MSOP PowerPAD package to effectively control self-heating. PowerPAD DESIGN CONSIDERATIONS The OPA1632 is available in a thermally-enhanced PowerPAD family of packages. These packages are constructed using a downset leadframe upon which the die is mounted (see Figure 3[a] and Figure 3[b]). This arrangement results in the lead frame being exposed as a thermal pad on the underside of the package (see Figure 3[c]). Because this thermal pad has direct thermal contact with the die, excellent thermal performance can be achieved by providing a good thermal path away from the thermal pad. DIE DIE Thermal Pad (a) Side View (b) End View (c) Bottom View Figure 3. Views of the Thermally-Enhanced Package. |
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Similar Description - OPA1632 |
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