Datasheet AD7711A (Analog Devices)

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LC2MOS Signal Conditioning ADC with RTD Current Source AD7711A* FEATURES FUNCTIONAL BLOCK DIAGRAM Charge Balancing ADC REF 24 Bits No Missing Codes REF AVDD DVDD IN (–) IN (+) VBIAS REF OUT
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0.0015% Nonlinearity AV 2-Channel Programmable Gain Front End DD Gains from 1 to 128 2.5V REFERENCE 4.5
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A Differential Inputs CHARGE-BALANCING A/D Low-Pass Filter with Programmable Filter Cutoffs CONVERTER Ability to Read/Write Calibration Coefficients AIN1(+) AUTO-ZEROED DIGITAL SYNC Bidirectional Microcontroller Serial Interface AIN1(–) M
S-D
PGA U MODULATOR FILTER Internal/External Reference Option AIN2(+) X AIN2(–) A = 1 – 128 Single- or Dual-Supply Operation MCLK Low Power (25 mW typ) with Power-Down Mode CLOCK IN AVDD GENERATION (7 mW typ) MCLK OUT 400
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A SERIAL INTERFACE APPLICATIONS RTD Transducers CONTROL OUTPUT REGISTER REGISTER RTD CURRENT GENERAL DESCRIPTION AD7711A
The AD7711A is a complete analog front end for low frequency measurement applications. The device accepts low level signals
AGND DGND V RFS TFS MODE SDATA SCLK DRDY A0 SS
directly from a transducer and outputs a serial digital word. It employs a sigma-delta conversion technique to realize up to CMOS construction ensures low power dissipation, and a soft- 24 bits of no missing codes performance. The input signal is ware programmable power-down mode reduces the standby applied to a proprietary programmable gain front end based power consumption to only 7 mW typical. The part is available around an analog modulator. The modulator output is pro- in a 24-lead, 0.3 inch-wide, hermetic dual-in-line package cessed by an on-chip digital filter. The first notch of this digital (CERDIP), as well as a 24-lead small outline (SOIC) package. filter can be programmed via the on-chip control register, allow- ing adjustment of the filter cutoff and settling time.
PRODUCT HIGHLIGHTS
The part features two differential analog inputs and a differen- 1. The programmable gain front end allows the AD7711A tial reference input. Normally, one of the channels will be used to accept input signals directly from an RTD transducer, as the main channel with the second channel used as an auxil- removing a considerable amount of signal conditioning. An iary input to periodically measure a second voltage. It can be on-chip current source provides the excitation current for operated from a single supply (by tying the VSS pin to AGND) the RTD. provided that the input signals on the analog inputs are more 2. The part features excellent static performance specifications positive than –30 mV. By taking the VSS pin negative, the part with 24-bit no missing codes, ± 0.0015% accuracy, and low can convert signals down to –VREF on its inputs. The part also rms noise (<250 nV). Endpoint errors and the effects of provides a 400 mA current source that can be used to provide temperature drift are eliminated by on-chip calibration excitation for RTD transducers. The AD7711A thus performs options, which remove zero-scale and full-scale errors. all signal conditioning and conversion for a single- or dual- channel system. 3. The AD7711A is ideal for microcontroller or DSP processor applications with an on-chip control register that allows The AD7711A is ideal for use in smart, microcontroller based control over filter cutoff, input gain, channel selection, signal systems. Input channel selection, gain settings, and signal polar- polarity, RTD current control, and calibration modes. ity can be configured in software by using the bidirectional serial port. The AD7711A contains self-calibration, system calibra- 4. The AD7711A allows the user to read and to write the tion, and background calibration options and allows the user to on-chip calibration registers. This means that the micro- read and write the on-chip calibration registers. controller has much greater control over the calibration procedure.
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Protected by U.S. Patent No. 5,134,401. REV. D Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise
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