AD7705| Datasheet

AD7705, AD7706

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3 V/5 V, 1 mW, 2-/3-Channel, 16-Bit, Sigma-Delta ADCs AD7705/AD7706
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 -, QSPITM-, MICROWIRETM-, 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 A maximum 16-lead PDIP, 16-lead SOIC, and 16-lead TSSOP packages

FUNCTIONAL BLOCK DIAGRAM
VDD REF IN( ) REF IN(+)

AD7705/AD7706
CHARGE BALANCING A/D CONVERTER ANALOG INPUT CHANNELS MAX BUFFER PGA A = 1 128 DIGITAL FILTER - MODULATOR

SERIAL INTERFACE REGISTER BANK MCLK IN MCLK OUT CLOCK GENERATION SCLK CS DIN

GENERAL DESCRIPTION
The AD7705/AD7706 1 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 serial digital output. The devices employ a - 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 onchip 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 w
hen 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.

DOUT
01166-001

GND

DRDY

RESET

Figure 1.

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 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 contains 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 W typ. These parts are available in a 16-lead, wide body (0.3 inch), plastic dual in-line package (DIP); a 16-lead, wide body (0.3
inch), standard small outline (SOIC) package; and a low profile, 16-lead, thin shrink small outline package (TSSOP).
1

Protected by U.S. Patent Number 5,134,401.

Rev. C
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