High Performance Automotive Sonar Intrusion – Data Sheet

AS8412

March 2001

Page 6 of 14

TX pulse

Echo in RX

44,4ms

0,6ms

Fig. 1 - Pulse/Echo Timing

Supply / Power-On Reset

The AS8412 requires a single 5-volt power supply. Pins for VDD and GND are separated for

the analog and digital circuits, and a 100 nF ceramic decoupling capacitor is recommended for

each pair.

There is an internal power-on-reset circuit that initializes the IC after each power-up. The VDD

rise time must be less than 20 ms, to guarantee proper initialization. Optionally, the IC can also

be reinitialized with a rising-edge at the pin 14, if requested by the application.

Time Reference

A clock must be present at the OSCIN input. The frequency may be selected to be either 40

kHz or 400 kHz, by setting the SEL40K input to ‘1’ or ‘0’ respectively. For the 40 kHz clock a

duty-cycle of approximately 50% is necessary.

The clock signal can be created in several possible ways:

• Generation by a microprocessor or other external circuit

• Built-in oscillator with an external 40-kHz crystal between OSCIN and OSCOUT. Depending

on the crystal, a load capacitor (about 22 pF) may be needed at OSCOUT.

• Built-in oscillator with an external 400-kHz ceramic resonator between OSCIN and

OSCOUT.

Load capacitors of at least 100 pF are necessary at the pins, according to the resonator speci-

100 pF capacitors).

Ultrasonic Transducers

The AS8412 is compatible with standard 40 kHz ultrasonic transducers, available from several

manufacturers. For each IC, one transducer is used to transmit the sonar pulses and one other

to receive the echoes reflected inside the vehicle. Internal lengths up to 3.5 meters can be cov-

ered.

In most applications, just two pairs of sensors will be used. The sensors will typically be posi-

tioned at the B-pillars (central pillars), close to the roof, to provide the best possible coverage of