AD4131-8

The AD4131-8 is an ultra-low power, high precision, measurement solution for low bandwidth battery operated applications. The fully integrated analog front end (AFE) includes a multiplexer for up to 16 single-ended or eight differential inputs, programmable gain amplifier (PGA), 16-bit sigma-delta (∑-Δ) analog-to-digital converter (ADC), on-chip reference and oscillator, selectable filter options, flexible sequencer, sensor biasing and excitation options, diagnostics, and newly added features to improve the battery-operated lifetime (duty cycling).

The AD4131-8 allows users to measure low frequency signals with a current consumption of 28.5 µA (gain = 1) and 32.5 µA (gain = 128) while continuously converting, and even lower average currents when using one of the duty cycling options. The AD4131-8 can be configured to have eight differential inputs or 16 single-ended or pseudodifferential inputs, which connect to a crosspoint multiplexer, where any input pair can become a measurement channel input to the PGA and ADC.

The AD4131-8 is designed to allow the user to operate from a single analog supply voltage from 1.71 V to 3.6 V. In battery applications, operation as low as 1.71 V can extend the system lifetime as the AFE can continue its operation, even as the battery voltage dissipates. The digital supply can be separate and range from 1.65 V to 3.6 V.

The following key analog functions are offered on the AD4131-8 to allow simple and effective connection to transducers used for measuring temperature, load, and pressure:

• PGA. Due to the programmable gain (from 1 to 128) and the high input impedance with low input current, the PGA allows direct interfacing to transducers with low output amplitudes like resistive bridges, thermocouples, and resistance temperature detectors (RTDs).
• The capacitive PGA allows full common-mode input range, giving designers greater margin for widely varying input common modes. A wider common-mode input range improves the overallresolution and is highly effective in ratio metric measurements.
• Low drift precision current sources. The IEXC0 and IEXC1 current source can be used to excite 2‑, 3‑, and 4‑wire RTDs. Excitation current output options include 100 nA, 10 µA, 20 µA, 50 µA, 100 µA, 150 µA, and 200 µA.
• The low-side power switch (PDSW) can be used to power down bridge sensors between conversions. The PDSW can be controlled within the sequencer on a per channel basis, allowing optimum timing and energy savings in the overall system. The PDSW can also allow higher powered analog sensors to be used in a low power system.
• Voltage bias for thermocouples (the VBIAS source sets the common-mode voltage of a channel to AV_DD/2).
• The flexible sequencer allows the conversion of each enabled preconfigured channel in a predetermined order, allowing a mix of transducer, system checks, and diagnostic measurements to be interleaved. The sequencer eliminates need for repetitive serial interface communication with the device. Sixteen channels can be configured in the sequence, each of them selecting from eight predefined ADC setups that allow selection of gain, filter type, output data rate, buffering, timing, and reference source.

High levels of integrated front-end functionality coupled with small package options allow smaller end solutions. For example, the AD4131-8 integrates a low thermal drift band gap reference in addition to accepting an external differential reference, which can be internally buffered.

In safety critical applications, the AD4131-8 includes diagnostic functionality such as open wire detection through burnout currents, internal temperature sensor, reference detection, and analog input overvoltage and undervoltage detection. Added diagnostics are included on the digital interface such as cyclic redundancy check (CRC) and serial interface checks for a robust communication link.

Applications

• Smart transmitters
• Wireless battery and harvester powered sensor nodes
• Portable instrumentation
• Temperature measurement: thermocouple, RTD, thermistors
• Pressure measurement: bridge transducers
• Healthcare and wearables