High Performance Automotive Sonar Intrusion – Data Sheet

AS8413

March 2001

Page 10 of 15

Table 2 shows some possible sensitivity combinations, marked according to the expected

behavior at the field. It should be used as a guide to determine the best combination for each

application.

Table 2. Sensitivity as Function of Digital and VCAP Programming

PROGRAM

390 pF

330 pF

270 pF

220 pF

High

OK

OK

+

+

Mid-high

-

OK

OK

+

Mid-low

-

-

OK

OK

Low

-

-

-

OK

(+) positions with higher sensitivities; may present false alarms under extreme conditions

(OK) most usual sensitivity combinations

(-) positions with lower sensitivities; may be useful for specific applications

The Self-Adjusting Sensitivity (SAS)

The SAS (Self-Adjusting Sensitivity) control loop is a powerful feature that optimizes the sensitiv-

ity to intrusion and motion, based on the present environmental conditions. Under quiet situations

the detector has a very high sensitivity. On the other hand, when certain disturbances such as

thermal gradients appear inside the vehicle, the sensitivity is drecreased to avoid possible false

alarms.

The sensitivity range programmed by the manufacturer is not changed by the SAS, that simply

selects the most adequate sensitivity for each situation within the allowed range. Fig. 5 gives a

rough idea of how the SAS can affect the detector sensitivity, for a given capacitor at VCAP.

HIGH

LOW

MID-LOW

MID-HIGH

SENSITIVITY

Fig. 5 - Sensitivity Ranges with SAS

The SAS actuation is controlled by the SAS input.

• SAS enabled (pin SAS = “1”):

After power-on, the IC starts with the lowest sensitivity within the programmed range. The

sensitivity will be constantly adjusted, according to the external conditions. Even under quiet

conditions, the IC may take at least 2 minutes to reach the maximum allowed sensitivity. That

should be considered during system evaluation.