CMS300 (in-plane) single-axis MEMS combi-sensor

The CMS300 measures angular rate about the Z-axis, which is perpendicular to the host PCBA, while its X and Y accelerometer axes remain parallel to the board. This arrangement provides one rotational channel and two linear-acceleration channels from a single surface-mounted device. A single CMS300 does not measure angular rate around all three rotational axes, so a multi-axis gyro design requires additional sensors or a complementary orthogonal configuration. The related CMS390 changes the package orientation so its rate axis lies parallel to the board. Engineers should therefore select the package orientation from the required system axes before finalising the PCB layout.

Select the lowest range that still accommodates the application’s maximum expected motion, including transient conditions and design margin. At ±150°/s, the gyro provides 0.005°/s nominal resolution and 204.8 lsb/(°/s), compared with 0.01°/s and 102.4 lsb/(°/s) at ±300°/s. The ±2.5g accelerometer range provides 0.079 mg resolution and 12,800 lsb/g, while the ±10g range provides 0.313 mg and 3,200 lsb/g. Gyro bandwidth options are 45, 55, 90 and 110 Hz, and acceleration options are 45, 62, 95 and 190 Hz. Independent channel settings allow noise, response time and overload margin to be balanced separately for each measurement axis.

The CMS300 operates functionally from 2.7 V to 3.6 V, although specified performance is defined over the narrower 3.15 V to 3.45 V interval. Its operating and start-up current are limited to 8 mA, excluding the initial charging current of external decoupling capacitors. Communication uses a four-wire SPI Mode 0 connection with 32-bit messages, a message rate from 1 Hz to 10 kHz and a clock frequency from 100 kHz to 7 MHz. The supply requires local 100 nF decoupling and a nearby 10 µF bulk capacitor, with a further 100 nF capacitor used for the internal reference. These limits should be incorporated into the processor timing, power-integrity and start-up design rather than treated as interchangeable nominal values.

The device operates from -40°C to +125°C, but individual drift specifications must be checked against their stated temperature intervals. Gyro bias variation is typically ±1.0°/s and no more than ±1.75°/s over temperature, while gyro scale-factor variation is typically below ±1% with a ±2.0% maximum. For the accelerometer, scale-factor variation is typically ±1% and can reach ±2.5%; bias behaviour also depends on whether the ±2.5g or ±10g range is selected. The published acceleration-bias variation figures of ±30 mg and up to ±75 mg are specified over -40°C to +85°C rather than the entire operating range. Designs requiring tighter absolute accuracy should therefore include temperature-aware calibration or system-level compensation.

The 10.4 × 6.0 × 2.2 mm ceramic LCC package is intended for conventional surface mounting, with maximum gyro and accelerometer misalignment stated as ±1.5% relative to the package. Signal or power tracks routed beneath the capacitive accelerometer can introduce an acceleration-bias offset, so the area below the package should be kept clear wherever possible. If routing beneath the device cannot be avoided, the resulting offset can be characterised and corrected at system level. The centre and side fixing pads provide mechanical attachment and must be soldered to electrically isolated PCB pads. Normal controlled placement is generally sufficient, but applications with tighter alignment requirements should include assembled-board calibration for residual cross-axis error.

The commanded built-in test applies defined offsets to the rate and acceleration outputs while also changing the BIT status indications. At 25°C, the nominal gyro response is +64°/s in the ±150°/s range and +107°/s in the ±300°/s range, while the nominal acceleration response is +1.25g or +6.2g depending on range. Temperature variation of these responses is bounded separately, allowing firmware to use range-dependent acceptance windows rather than a single fixed threshold. The BIT output pin and SPI status messages can identify internal faults, invalid commands, SPI clock errors and NVM errors. A practical implementation should run checks at start-up and at controlled intervals when the temporary test offset will not interfere with normal control functions.

Ultrasonic cleaning must not be used because acoustic energy can excite the MEMS structure at or near its natural resonance. Assembly should follow the defined reflow profile and specified pad arrangement, without estimating process values from package or profile drawings. The hermetically sealed ceramic package is rated for operation up to 90% relative humidity under non-condensing conditions. Mechanical limits include 95g operating shock for a 6 ms half-sine pulse and 10,000g unpowered shock for 0.5 ms, while ESD protection is rated at 2 kV HBM and 250 V CDM. For volume assembly, the device is available in tape-and-reel packaging with up to 1,500 units per reel.