LY550ALH

Terminology

Doc ID 15802 Rev 2

7/12

3

Terminology

3.1

Sensitivity

An angular rate gyroscope is a device that produces a positive-going output voltage for

counterclockwise rotation around the sensitive axis considered. Sensitivity describes the

gain of the sensor and can be determined by applying a defined angular velocity to it. This

value changes very little over temperature and time.

3.2

Zero-rate level

Zero-rate level describes the actual output signal if there is no angular rate present. The

zero-rate level of precise MEMS sensors is, to some extent, a result of stress to the sensor

and therefore zero-rate level can slightly change after mounting the sensor onto a printed

circuit board or after exposing it to extensive mechanical stress. This value changes very

little over temperature and time.

3.3

Self-test

Self-test allows testing of the mechanical and electrical part of the sensor, allowing the

seismic mass to be moved by means of an electrostatic test-force. The self-test function is

off when the ST pin is connected to GND. When the ST pin is tied to Vdd, an actuation force

is applied to the sensor, emulating a definite Coriolis force. In this case the sensor output will

exhibit a voltage change in its DC level which is also dependent on the supply voltage.

When ST is active, the device output level is given by the algebraic sum of the signals

produced by the velocity acting on the sensor and by the electrostatic test-force. If the output

signals change within the amplitude specified in

Table 3, then the mechanical element is

working properly and the parameters of the interface chip are within the defined

specifications.

3.4

High pass filter reset (HP)

The LY550ALH provides the possibility to reset the optional external high pass filter by

applying a high logic value to the HP pad. This procedure ensures faster response,

especially during overload conditions. Moreover, this operation is suggested each time the

device is powered.