Analog Devices Analog to Digital Converter AD7705


The AD7705/AD7706 are complete analog front ends for low-frequency measurement applications. These 2-/3-channel devices can accept low-level input signals directly from a transducer and produce a serial digital output. The devices employ a Σ-Δ conversion technique to realize up to 16 bits of no missing codes performance. The selected input signal is applied to a proprietary, programmable-gain front end based around an analog modulator. The modulator output is processed by an on-chip digital filter. The first notch of this digital filter can be programmed via an on-chip control register, allowing adjustment of the filter cutoff and output update rate. The AD7705/AD7706 devices operate from a single 2.7 V to 3.3 V or 4.75 V to 5.25 V supply. The AD7705 features two fully differential analog input channels; the AD7706 features three pseudo differential input channels. Both devices feature a differential reference input. Input signal ranges of 0 mV to 20 mV through 0 V to 2.5 V can be incorporated on both devices when operating with a VDD of 5 V and a reference of 2.5 V. They can also handle bipolar input signal ranges of ±20 mV through ±2.5 V, which are referenced to the AIN(−) inputs on the AD7705 and to the COMMON input on the AD7706.

 117,40

FEATURES

  • AD7705: 2 fully differential input channel ADCs
  • AD7706: 3 pseudo-differential input channel ADCs
    • 16 bits no missing codes
    • 0.003% nonlinearity
  • Programmable gain front end: gains from 1 to 128
  • 3-wire serial interface
    • SPI®-, QSPI™-, MICROWIRE™-, and DSP-compatible
    • Schmitt-trigger input on SCLK
  • Ability to buffer the analog input
  • 2.7 V to 3.3 V or 4.75 V to 5.25 V operation
  • Power dissipation 1 mW maximum @ 3 V
  • Standby current 8 μA maximum
  • 16-lead PDIP, 16-lead SOIC, and 16-lead TSSOP packages

GENERAL DESCRIPTION

The AD7705/AD7706 are complete analog front ends for low-frequency measurement applications. These 2-/3-channel devices can accept low-level input signals directly from a transducer and produce a serial digital output. The devices employ a Σ-Δ conversion technique to realize up to 16 bits of no missing codes performance. The selected input signal is applied to a proprietary, programmable-gain front end based around an analog modulator. The modulator output is processed by an on-chip digital filter. The first notch of this digital filter can be programmed via an on-chip control register, allowing adjustment of the filter cutoff and output update rate.

The AD7705/AD7706 devices operate from a single 2.7 V to 3.3 V or 4.75 V to 5.25 V supply. The AD7705 features two fully differential analog input channels; the AD7706 features three pseudo differential input channels.

Both devices feature a differential reference input. Input signal ranges of 0 mV to 20 mV through 0 V to 2.5 V can be incorporated on both devices when operating with a VDD of 5 V and a reference of 2.5 V. They can also handle bipolar input signal ranges of ±20 mV through ±2.5 V, which are referenced to the AIN(−) inputs on the AD7705 and to the COMMON input on the AD7706.

The AD7705/AD7706 devices, with a 3 V supply and a 1.225 V reference, can handle unipolar input signal ranges of 0 mV to 10 mV through 0 V to 1.225 V. The devices can accept bipolar input ranges of ±10 mV through ±1.225 V. Therefore, the AD7705/AD7706 devices perform all signal conditioning and conversion for a 2-channel or 3-channel system.

The AD7705/AD7706 are ideal for use in the smart, microcontroller, or DSP-based systems. The devices feature a serial interface that can be configured for 3-wire operation. Gain settings, signal polarity, and update rate selection can be configured in software using the input serial port. The parts contain self-calibration and system calibration options to eliminate gain and offset errors on the part itself or in the system. CMOS construction ensures very low power dissipation, and the power-down mode reduces the standby power consumption to 20 μW types.

These parts are available in a 16 lead, wide-body (0.3 inches), plastic dual in-line package (DIP); a 16-lead, wide-body (0.3 inches), standard small outline (SOIC) package; and a low profile, 16-lead, thin shrink small outline package (TSSOP).

 

PRODUCT HIGHLIGHTS

  • The AD7705/AD7706 devices consume less than 1 mW at 3 V supplies and a 1 MHz master clock, making them ideal for use in low power systems. Standby current is less than 8 μA.
  • The programmable gain input allows the AD7705/AD7706 to accept input signals directly from a strain gage or transducer, removing a considerable amount of signal conditioning.
  • The AD7705/AD7706 are ideal for microcontroller or DSP processor applications with a 3-wire serial interface, reducing the number of interconnect lines and reducing the number of optocouplers required in isolated systems. The parts feature excellent static performance specifications with 16 bits, no missing codes, ±0.003% accuracy, and low RMS noise (<600 nV). Endpoint errors and the effects of temperature drift are eliminated by on-chip calibration options, which remove zero-scale and full-scale errors.
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