CAS290 series (dual-axis, orthogonal) high-perfomance linear accelerometers

Choose the lowest range that still covers normal acceleration, expected transients and an appropriate design margin, because the lower-range variants provide greater output sensitivity and lower measurement thresholds. CAS291 covers ±0.85 g with 33,500 lsb/g, 1,150 mV/g, a 0.03 mg threshold and noise density of no more than 50 µg/√Hz. CAS292 and CAS293 extend the range to ±2.5 g and ±10 g while retaining 0.10 mg thresholds. CAS294 and CAS295 cover ±30 g and ±96 g, but their thresholds rise to 0.30 mg and 1.0 mg respectively. Model worst-case shock and vibration before selecting the range rather than basing the decision solely on nominal acceleration.

Use the analogue output when the host system already includes suitable high-resolution conversion or requires the sensor’s bandwidth above 250 Hz. Its scale factor is ratiometric and varies from 1,150 mV/g on CAS291 to 10 mV/g on CAS295, so ADC range, reference stability and input noise must be considered together. The digital interface offers bandwidth above 170 Hz, direct scale factors from 33,500 to 300 lsb/g and access to temperature and built-in test status. It also avoids adding an external ADC solely for the acceleration channels. The final choice therefore depends on bandwidth, conversion accuracy, processing architecture and the diagnostic data required by the host.

Use a 2.7 V to 3.6 V supply for functional operation, but keep Vdd within 3.15 V to 3.45 V when the stated performance limits must be met. The nominal operating point is 3.3 V, with typical current consumption of 3 mA across the range. Allow up to 20 ms for start-up and up to 10 ms to recover from an over-range or shock event before accepting measurement data. The interface design should follow the defined local decoupling arrangement and keep supply impedance low during start-up. This gives the host a clear power-good and data-valid sequence and avoids treating transient output behaviour as valid acceleration.

The orthogonal package places the two MEMS sense axes in a different orientation from a flat-mounted dual-axis accelerometer. When the side-mounted CAS290 is combined with an in-plane sensing arrangement, three degrees of freedom can be measured on one PCBA without installing a separate perpendicular board. The package measures 10.4 × 6.7 × 2.7 mm and has a typical mass of 0.6 g, so mechanical placement and solder-fixture control remain important. Typical package misalignment is ±25 mrad when suitable fixtures are used, while internal axis orthogonality is 1.7 mrad. System calibration should still resolve the installed axis matrix rather than assume perfect geometric alignment.

The CAS290 series operates from -40 °C to +125 °C and can be stored from -55 °C to +150 °C, with humidity limited to 90% RH under non-condensing conditions. The operating shock rating is 1,000 g for a 1 ms half-sine pulse. Non-operating shock capability is 6,500 g for CAS291 through CAS293 and 10,000 g for CAS294 and CAS295, using a 0.1 ms half-sine pulse. These are limit conditions rather than recommended continuous operating points, and prolonged exposure near absolute ratings can affect performance or reliability. The equipment-level design should therefore include mounting, enclosure and vibration controls appropriate to the actual mechanical environment.

Separate initial offset from repeatability, thermal drift, long-term stability and vibration-induced bias. Bias run-to-run variation ranges from ±0.35 mg on CAS291 to ±8.0 mg on CAS295, while one-year bias stability ranges from ±7.5 mg to ±75 mg. Bias variation across -40 °C to +125 °C is ±50 mg for CAS291–CAS293, ±150 mg for CAS294 and ±500 mg for CAS295. The analogue outputs sit nominally around Vdd/2 and may carry a fixed device offset, while the digital channel has its own bias setting error; both can be reduced through system calibration. The remaining error model should include scale-factor temperature variation of ±1.2% and the stated vibration rectification for the selected range.

The digital interface is a four-wire SPI slave operating in Mode 0, with each transaction carrying six bytes or 48 bits. A 1 kHz message rate and 1 MHz clock are nominal; the supported ranges are 1 Hz to 10 kHz for messages and 100 kHz to 8 MHz for the clock. Sampling above 500 Hz is recommended when aliasing is a concern, although the application must still provide filtering suited to its measurement bandwidth. Separate requests provide X/Y acceleration data or status and temperature data, and the command format can enable commanded built-in test. Data_Out is tri-stated when slave select is high, which supports a shared bus when chip-select timing and checksum handling are implemented correctly.

Because the CAS290 series uses capacitive MEMS sensing, conductive tracks routed beneath the package can introduce an acceleration bias offset. Signal and power routing should therefore be kept away from the package footprint where practical, including connections running towards shared supply star points. If routing beneath the device cannot be avoided, the installed offset should be measured and removed through higher-level system compensation. The centre and side fixing pads are mechanical connections and should be soldered to electrically isolated pads. Controlled placement fixtures, axis-orientation checks and a gravity-based calibration can reduce errors associated with package misalignment and assembly tolerances.