AD22282-A-R2: Self Test

Q 

Which function has the self-test pin? I studied the data sheet and tried it
out, but I do not understand it.

 

A 

The self test feature designed in all of our inertial sensors activates the
mechanical structure of the device which in turns generates a signal through
the electronic portion of the chip, thereby allowing the user to verify proper
operation of the entire device. 

By applying a logic 1 signal on the ST pin, a voltage is applied on special
self test 'fingers' located around the moving element of the sensor.  This
voltage creates an electrostatic force which causes the structure to move.  The
sensor displacement generates an electrical signal on the sensing fingers, as
if the sensor were moved under normal acceleration. 
The signal is processed through the signal conditioning circuitry and appears
at the output of the device.  The self test feature therefore exercises every
part of the chip.  A proper output signal is therefore indicative that the
entire sensor is functional. 

The self test feature cannot be used to verify drift of the device.  It should
not be used to verify parametric compliance.  It should only be used to verify
functionality.  If changes such as drift over temperature cannot be tolerated
in the application, these need to be addressed through calibration or
temperature compensation routines.


This ST pin may be left open circuit or connected to common (COM) in normal
use.