High Performance Automotive Sonar Intrusion – Data Sheet

AS8412

March 2001

Page 12 of 14

The blockage and saturation are signalized just one time at each occurrence, to avoid continu-

ous alarm triggering. Detection of glass breakage by saturation is not guaranteed.

Table 3. Disturbances detected by the AS8412

LED

ALARM

WARN

Conditions

pulsing

1

1

no disturbance

pulsing

1

0

weak intrusion

0

0

0

intrusion

pulsing

0

1

blockage

0

0

1

saturation

WARN

ALARM

Fig. 7 - Weak Intrusion followed by an Intrusion

Courtesy Entry/Exit Time

The pin ALEN is an optional alarm enable input that can be used to provide a courtesy entry

and/or exit time. When tied to VDD, normal alarm operation is enabled. If ALEN is grounded,

the outputs ALARM, WARN and LED are disabled, except during the self-test, when LED indi-

cates the test result.

By grounding ALEN, the IC can be made inoperative as seen by the control unit and still keeps

its internal processing. This is useful when intrusion detections must be temporarily inhibited,

or to block self-test pulses at ALARM and WARN.

During the first 10 or 20 seconds after shutting a door in a hot and sunny day, an alarm indica-

tion may occur, due to thermal gradients inside the vehicle. That should be considered when

choosing a courtesy time for an AS8412-based system. When an RC circuit connected to the

supply voltage is applied to ALEN, the courtesy time after power-up is given by:

T

≈0.92 x R x C