説明

The LT1994 is a high precision, very low noise, low distortion, fully differential input/output amplifi er optimized for 3V, single-supply operation. The LT1994’s output common mode voltage is independent of the input common mode voltage, and is adjustable by applying a voltage on the VOCM pin. A separate internal common mode feedback path provides accurate output phase balancing and reduced even-order harmonics. This makes the LT1994 ideal for level shifting ground referenced signals for driving differential input, single-supply ADCs.The LT1994 output can swing rail-to-rail and is capable of sourcing and sinking up to 85mA. In addition to the low distortion characteristics, the LT1994 has a low input referred voltage noise of 3nV/√Hz. This part maintains its performance for supply voltages as low as 2.375V. It draws only 13.3mA of supply current and has a hardware shutdown feature that reduces current consumption to 225μA.The LT1994 is available in an 8-pin MSOP or 8-pin DFN package.

 

特徴

Fully Differential Input and Output

Wide Supply Range: 2.375V to 12.6V

Rail-to-Rail Output Swing

Low Noise: 3nV/√Hz

Low Distortion, 2VP-P, 1MHz: –94dBc

Adjustable Output Common Mode Voltage

Unity-Gain Stable

Gain-Bandwidth: 70MHz

Slew Rate: 65V/μs

Large Output Current: 85mA

DC Voltage Offset <2mV Max

Open-Loop Gain: 100V/mV

Low Power Shutdown

8-Pin MSOP or 3mm × 3mm DFN Package

 

アプリケーション

Differential Input A/D Converter Driver

Single-Ended to Differential Conversion

Differential Amplifi cation with Common Mode Translation

Rail-to-Rail Differential Line Driver/Receiver

Low Voltage, Low Noise, Differential Signal Processing

 

アプリケーション情報

Functional Description

The LT1994 is a small outline, wideband, low noise and low distortion fully-differential amplifi er with accurate output-phase balancing. The LT1994 is optimized to drive low voltage, single-supply, differential input analog-to-digital converters (ADCs). The LT1994’s output is capable of swinging rail-to-rail on supplies as low as 2.5V, which makes the amplifi er ideal for converting ground referenced, single-ended signals into VOCM referenced differential signals in preparation for driving low voltage, single-supply, differential input ADCs. Unlike traditional op amps which have a single output, the LT1994 has two outputs to process signals differentially. This allows for two times the signal swing in low voltage systems when compared to single-ended output amplifi ers. The balanced differential nature of the amplifi er also provides even-order harmonic distortion cancellation, and less susceptibility to common mode noise (like power supply noise). The LT1994 can be used as a single-ended input to differential output amplifi er, or as a differential input to differential output amplifier.The LT1994’s output common mode voltage, defi ned as the average of the two output voltages, is independent of the input common mode voltage, and is adjusted by applying a voltage on the VOCM pin. If the pin is left open, there is an internal resistive voltage divider, which develops a potential halfway between the V+ and V– pins. The VOCM pin will have an equivalent Thevenin equivalent resistance of 40k, and a Thevenin equivalent voltage of half supply. Whenever this pin is not hard tied to a low impedance ground plane, it is recommended that a high quality ceramic capacitor is used to bypass the VOCM pin to a low impedance ground plane (see Layout Considerations in this document). The LT1994’s internal common mode feedback path forces accurate output phase balancing to reduce even order harmonics, and centers each individual output about the potential set by the VOCM pin. The outputs (OUT+ and OUT–) of the LT1994 are capable of swinging rail-to-rail. They can source or sink up to approximately 85mA of current. Each output is rated to drive approximately 25pF to ground (12.5pF differentially). Higher load capacitances should be decoupled with at least 25Ω of series resistance from each output.