GENERAL DESCRIPTION

The AD7730 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 part 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 230,000 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 AD7730 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 AD7730 is available in a 24-pin plastic DIP, a 24-lead SOIC and 24-lead TSSOP package. The AD7730L is available in a 24-lead SOIC and 24-lead TSSOP package.

KEY FEATURES

Resolution of 230,000 Counts (Peak-to-Peak)

Offset Drift: 5 nV/°C

Gain Drift: 2 ppm/°C

Line Frequency Rejection: >150 dB

Buffered Differential Inputs

Programmable Filter Cutoffs

Specified for Drift Over Time

Operates with Reference Voltages of 1 V to 5 V

ADDITIONAL FEATURES

Two-Channel Programmable Gain Front End

On-Chip DAC for Offset/TARE Removal

FASTStep? Mode

AC or DC Excitation

Single Supply Operation

APPLICATIONS

Weigh Scales

Pressure Measurement