Analog Devices Inc./Maxim Integrated

The AD7708/18 are complete analog front-ends for low frequency measurement applications. The AD7718 contains a 24-bit sigma delta ADC with PGA and can be configured as 4/5 fully-differential input channels or 8/10 pseudo-differential input channels. Two pins on the device are configurable as analog inputs or reference inputs. The AD7708 is a 16-bit version of the AD7718. Inputs signal ranges from 20mV to 2.56V can be directly converted using these ADCs. Signals can be converted directly from a transducer without the need for signal conditioning.

The AD7719 is a complete analog front-end for low frequency measurement applications. It contains two high-resolution sigma delta ADCs, switchable matched excitation current sources, low-side power switches, digital I/O port and temperature sensor. The 24-bit main channel with PGA accepts fully differential, unipolar and bipolar input signal ranges from REFIN1/128 to REFIN1. Signals can be converted directly from a transducer without the need for signal conditioning. The 16-bit aux channel does not have a PGA and has an input signal range of REFIN2 or REFIN2/2.

The AD7722 is a complete low power, 16-bit, sigma-delta ADC. The part operates from a +5 V supply and accepts a differential input voltage range of 0 V to +2.5 V or ±1.25 V centered around a common-mode bias. The AD7722 provides 16-bit performance for input bandwidths up to 90.625 kHz. The part provides data at an output word rate of 195.3 kHz.The analog input is continuously sampled by an analog modulator eliminating the need for external sample-and-hold circuitry. The modulator output is processed by two Finite Impulse Response (FIR) digital filters in series. The on-chip filtering reduces the external antialias requirements to first order, in most cases. The group delay for the filter is 215.5 µs, while the settling time for a step input is 431 µs. The sample rate, filter corner frequency, and output word rate are set by an external clock that is nominally 12.5 MHz.Use of a single bit DAC in the modulator guarantees excellent linearity and dc accuracy. Endpoint accuracy is ensured by on-chip calibration. This calibration procedure minimizes the zero-scale and full-scale errors.Conversion data is provided at the output register through a flexible serial port or a parallel port. This offers 3-wire, high speed interfacing to digital signal processors. The serial interface operates in an internal clocking (master) mode, whereby an internal serial data clock and framing pulse are device outputs. Additionally, two AD7722s can be configured with the serial data outputs connected together. Each converter alternately transmits its conversion data on a shared serial data line.The part provides an accurate on-chip 2.5 V reference. A reference input/output function is provided to allow either the internal reference or an external system reference to be used as the reference source for the part.The AD7722 is available in a 44-pin PQFP package and is specified over the industrial temperature range from –40°C to +85°C.

The AD7730L is a complete analog front end for weigh-scale and pressure measurement applications. The device accepts low-level signals directly from a transducer and outputs a serial digital word. The input signal is applied to a proprietary programmable gain front end based around an analog modulator. The modulator output is processed by a low pass programmable digital filter, allowing adjustment of filter cutoff, output rate and settling time.The part features two buffered differential programmable gain analog inputs as well as a differential reference input. The device operates from a single +5 V supply. It accepts four unipolar analog input ranges: 0 mV to +10 mV, +20 mV, +40 mV and +80 mV and four bipolar ranges: ±10 mV, ±20 mV, ±40 mV and ±80 mV. The peak-to-peak resolution achievable directly from the part is 1 in 110,000 counts. An on-chip 6-bit DAC allows the removal of TARE voltages. Clock signals for synchronizing ac excitation of the bridge are also provided.The serial interface on the part can be configured for three-wire operation and is compatible with microcontrollers and digital signal processors. The AD7730L contains self-calibration and system calibration options, and features an offset drift of less than 5 nV/°C and a gain drift of less than 3 ppm/°C. The part is available in a 24-lead SOIC and 24-lead TSSOP package. It is a lower power version of the AD7730 (approximately 1/3 the power).

The AD7731 is a complete analog front-end for process control applications. The device has a proprietary programmable gain front end that allows it to accept a range of input signal ranges, including low level signals, directly from a transducer. The sigma-delta architecture of the part consists of an analog modulator and a low pass programmable digital filter, allowing adjustment of filter cutoff, output rate and settling time.The part features three buffered differential programmable gain analog inputs (which can be configured as five pseudo-differential inputs), as well as a differential reference input. The part operates from a single +5 V supply and accepts seven unipolar analog input ranges: 0 to +20 mV, +40 mV, +80 mV, +160 mV, +320 mV, +640 mV and +1.28 V, and seven bipolar ranges: ±20 mV, ±40 mV, ±80 mV, ±160 mV, ±320 mV, ±640 mV and ±1.28 V. The peak-to-peak resolution achievable directly from the part is 16 bits at an 800 Hz output rate. The part can switch between channels with 1 ms settling time and maintain a performance level of 13 bits of peak-to-peak resolution.The serial interface on the part can be configured for three-wire operation and is compatible with microcontrollers and digital signal processors. The AD7731 contains self-calibration and system calibration options and features an offset drift of less than 5 nV/°C and a gain drift of less than 2 ppm/°C.The part is available in a 24-lead plastic DIP, a 24-lead SOIC and 24-lead TSSOP package.APPLICATIONSProcess ControlPLCs/DCSIndustrial Instrumentation