Low Power 24-Bit Sigma-Delta A/D Converter for Bridge Sensors

The AD7796/AD7797 are complete, analog front ends for high precision, bridge sensor applications such as weigh scales. The AD7796/AD7797 contain a Σ-∆ ADC capable of 16-/24-bit resolution, respectively. The on-chip instrumentation amplifier has a fixed gain of 128, allowing small amplitude signals such as those from bridge sensors to be directly interfaced to the ADC.

Each device has one differential input and contains a temperature sensor that is internally connected to the ADC. This sensor can be used to perform temperature compensation of the bridge.

The devices can be operated with the internal clock or an external clock. The output data rate from the devices is software-programmable and can be varied from 4.17 Hz to 123 Hz.

The AD7796/AD7797 operate with a power supply from 2.7 V to 5.25 V. Each device consumes a current of 250 µA typical and is housed in a 16-lead TSSOP.

Applications

* Weigh scales

* Strain gages

* Industrial process control

* Instrumentation

* Portable instrumentation

* RMS noise: 65 nV

* Instrumentation amp

* Temperature sensor

* Internal clock oscillator

* Simultaneous 50 Hz/60 Hz rejection

* Update rate range: 4.17 Hz to 123 Hz

* Current: 250 µA typ

* Power-down: 1 µA

* Power supply range: 2.7 V to 5.25 V

* –40°C to +85°C temperature range

* Independent interface power supply

* 16-lead TSSOP