FXLS8964AF datasheet(9/98 Pages) NXP

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NXP Semiconductors

FXLS8964AF

3-Axis Low-g Accelerometer

FXLS8964AF

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Objective data sheet

Rev. 2 — 30 October 2020

9 / 98

9 Mechanical and electrical specifications

9.1 Definitions

Sensitivity

The accelerometer sensitivity, also known as scale-factor, represents the change in

acceleration input corresponding to 1 LSB change in output and is typically measured in

either mg/LSB or LSB/g.

Zero-g offset

The accelerometer zero-g offset describes the deviation of the sensor output from the

ideal values when it is stationary in earth's 1 g gravitational field. With an accelerometer

stationary and placed on a level, horizontal surface, the ideal output is 0 g for the X

and Y axes, and 1 g for the Z-axis. The deviation of each output from the ideal value is

called zero-g offset. Offset is, to some extent, a result of stress on the sensor and how

well the sensor is leveled when soldered to the board. Therefore, the zero-g offset can

change after mounting the sensor onto a printed circuit board or exposing it to extensive

mechanical stress.

For applications that require increased precision, any residual post-board mount offset

may be removed using the

OFF_X/Y/Z registers, or alternatively, in the host application

software.

Self-Test

The integrated self-test function can be used to verify correct transducer and signal chain

operation without the need to apply an external acceleration stimulus. When the self-

test function is activated for each axis, an electrostatic actuation force is applied to the

proof mass, simulating a small change in acceleration. The device's self-test function is

independently exercisable for each axis, along with a selectable displacement direction

(polarity). The device need not be static while exercising the self-test function as it is

insensitive to any external physical acceleration. Refer to AN5311 for more details on

self-test.

Noise density and RMS integrated noise

Noise density is defined as the noise per unit of square root bandwidth and is typically

expressed in units of mg/√Hz or μg/√Hz for a consumer grade accelerometer. Noise is

measured with the device held stationary in a 1g field and isolated from environmental

noise and mechanical vibration. The RMS noise at a given ODR can be estimated as

follows:

Nrms = ND * √BW

For example, in the ±2 g FSR, operating in HPM with an ODR of 400 Hz, the estimated

RMS noise would be:

Nrms = 280 µg/√Hz * √(400/2) Hz = 3.96 mg (~ 4 LSB).

Cross-axis sensitivity

Cross-axis sensitivity is the ratio of the measured acceleration for an axis to the input

acceleration along each axis orthogonal to the measured axis. Cross-axis sensitivity

leads to undesirable nonorthogonality of X, Y and Z axes in the frame of reference of

the assembled device when mapping to other frames of reference. Cross-axis sensitivity

is expressed as a percentage of the orthogonal input acceleration with six separate

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