a FEATURES Charge Balancing ADC 24 Bits No Missing Codes ؎0.0015% Nonlinearity Two-Channel Programmable Gain Front End Gains from 1 to 128 Differential Inputs Low-Pass Filter with Programmable Filter Cutoffs Ability to Read/Write Calibration Coefficients Bidirectional Microcontroller Serial Interface Internal/External Reference Option Single or Dual Supply Operation Low Power (25 mW typ) with Power-Down Mode (7 mW typ} APPLICATIONS Weigh Scales Thermocouples Process Control Smart Transmitters Chromatography
LC2MOS Signal Conditioning ADC AD7710* FUNCTIONAL BLOCK DIAGRAM AV DD
REF IN (–)
REF IN (+)
AV DD 2.5V REFERENCE
CHARGE-BALANCING A/D CONVERTER
M U X
AUTO-ZEROED ∑-∆ MODULATOR
A = 1 – 128 AIN2(–) AV DD
CLOCK GENERATION 20µA
SERIAL INTERFACE CONTROL REGISTER
RFS TFS MODE SDATA SCLK DRDY A0
The AD7710 is a complete analog front end for low frequency measurement applications. The device accepts low level signals directly from a strain gage or transducer and outputs a serial digital word. It employs a sigma-delta conversion technique to realize up to 24 bits of no missing codes performance. The 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 the on-chip control register allowing adjustment of the filter cutoff and settling time. The part features two differential analog inputs and a differential reference input. Normally, one of the channels will be used as the main channel with the second channel used as an auxiliary input to periodically measure a second voltage. It can be operated from a single supply (by tying the VSS pin to AGND) provided that the input signals on the analog inputs are more positive than –30 mV. By taking the VSS pin negative, the part can convert signals down to –VREF on its inputs. The AD7710 thus performs all signal conditioning and conversion for a single or dual channel system. The AD7710 is ideal for use in smart, microcontroller based systems. Input channel selection, gain settings and signal polarity can be configured in software using the bidirectional serial port. The AD7710 contains self-calibration, system calibration and background calibration options and also allows the user to read and write the on-chip calibration registers.
CMOS construction ensures low power dissipation and a software programmable power down mode reduces the standby power consumption to only 7 mW typical. The part is available in a 24-pin, 0.3 inch-wide, plastic and hermetic dual-in-line package (DIP) as well as a 24-lead small outline (SOIC) package. PRODUCT HIGHLIGHTS
1. The programmable gain front end allows the AD7710 to accept input signals directly from a strain gage or transducer, removing a considerable amount of signal conditioning. 2. The AD7710 is ideal for microcontroller or DSP processor applications with an on-chip control register which allows control over filter cutoff, input gain, channel selection, signal polarity and calibration modes. 3. The AD7710 allows the user to read and write the on-chip calibration registers. This means that the microcontroller has much greater control over the calibration procedure. 4. No missing codes ensures true, usable, 23-bit dynamic range coupled with excellent ± 0.0015% accuracy. The effects of temperature drift are eliminated by on-chip self-calibration, which removes zero-scale and full-scale errors.
- Protected by U.S. Patent No. 5,134,401.
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