Features and Benefits
- Two Fully Differential Input Channel ADCs
- Programmable Gain Front End Gains from 1 to 128
- Three-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 max @ 3 V
- Standby Current 8 µA max
- 16-Lead DIP, 16-Lead SOIC and TSSOP Packages
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 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 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 μW 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).
Product Lifecycle Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Evaluation Kits (1)
The EVAL-AD7705EBZ is a fully featured evaluation Board for the AD7705. The evaluation board can be connected to a PC via the parallel port. Software is provided enabling the user to perform detailed analysis of the ADC's performance.
Documentation & Resources
AN-282: Fundamentals of Sampled Data Systems2/14/2015
AN-342: Analog Signal-Handling for High Speed and Accuracy2/14/2015
AN-202: An IC Amplifier User’s Guide to Decoupling, Grounding, and Making Things Go Right for a Change (Rev. B)2/14/2015
AN-280: Mixed Signal Circuit Technologies2/14/2015
AN-389: Using Sigma-Delta Converters-Part 22/14/2015
AN-388: Using Sigma-Delta Converters-Part 12/14/2015
AN-347: Shielding and Guarding2/14/2015
AN-311: How to Reliably Protect CMOS Circuits Against Power Supply Overvoltaging3/8/2008
AN-607: Selecting a Low Bandwidth (<15 kSPS) Sigma-Delta ADC (Rev. E)10/12/2006
AN-615: Peak-to-Peak Resolution Versus Effective Resolution (Rev. 0)12/21/2004
AN-101: Cross Plot Generator Allows Quick A/D Converter Evaluation12/12/2002
AN-397: Electrically Induced Damage to Standard Linear Integrated Circuits:11/18/2002
AN-283: Sigma-Delta ADCs and DACs9/24/2002
Designing Power Supplies for High Speed ADC2/1/2012
Delta-Sigma Rocks RF, As ADC Designers Jump On Jitter1/12/2006
Part 2: Circuit Suggestions Using Features and Functionality of New Sigma-Delta ADCs6/1/2002
Part 1: Circuit Suggestions Using Features and Functionality of New Sigma-Delta ADCs10/1/2001
Tools & Simulations
AD7705 Companion Parts
Recommended Digital Isolators
- For isolated USB designs in healthcare and industrial control: ADUM4160.
- For cost sensitive designs: ADUM7440, ADUM7441, ADUM7442.
- For digital isolators with integrated isolated power: ADUM5401, ADUM5402, ADUM5403.
- For process control applications: ADUM1400, ADUM1200.
Recommended Voltage References
ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.
Sample & Buy
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Pricing displayed is based on 1-piece. The USA list pricing shown is for budgetary use only, shown in United States dollars (FOB USA per unit), and is subject to change. International prices may vary due to local duties, taxes, fees and exchange rates.