ams AS8413 High performance automotive sonar intrusion Datasheet

AS8413
HIGH PERFORMANCE
AUTOMOTIVE SONAR INTRUSION
Data Sheet
March 2001
High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
Key Features
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True sonar/pulse-echo operation
Master/slave synchronization
Wide dynamic range
Programmable sensitivity levels
Self-adaptive to vehicle interiors
Self-adaptive to temperature and environmental changes
High sensitivity to intrusion
Immunity to false alarms
Detection of sabotage attempts
Compatible with standard 40 kHz ultrasonic transducers
Specific for systems with multiple transducers
No adjustments needed at factory or at field
Few external components
Time reference: external clock or oscillator based on crystal/ceramic resonator
Built-in self-test
Internal power-on-reset
Advanced CMOS technology
Low power consumption: 0.65 to 1.0 mA
Operation between -40°C and +85 °C
Available in 24-pin DIP and 24-pin SOIC package
General Description
The AS8413 is a signal processing IC designed to implement reliable, high-performance
sonar intrusion detectors. It generates short 40 kHz bursts to feed an ultrasonic transducer. The resulting sonar waves are reflected on the vehicle interior and the echoes are
received by another transducer. Inside the AS8413, the electrical signal is first submitted to
an analog conditioning circuit, then it is digitized and processed by a DSP, whose output is
analyzed by a discriminator based on fuzzy-logic techniques. Thus, true intrusion conditions can be discerned from natural phenomena and other allowable disturbances.
Synchronization between the sonar waves from 2 or more pairs of transducers is made
possible by means of a master/slave configuration. Each pair is controlled by a AS8413 IC.
No adjustments are necessary at factory or at the field, as the AS8413 is self-adaptive to
the physical and environmental conditions. Compact and EMI-resistant intrusion detectors
are made possible, due to the small number of components.
Block Diagram
VCAP
RX
TX1
TX2
SEL40K
OSCIN
OSCOUT
PREAMP
MODULATOR /
DRIVER
OSCILLATOR
BAND-PASS
FILTER
AGC
CONTROL
LOGIC
ENVELOPE
DETECTOR
DSP
A/D
CONVERTER
DISCRIMINATOR
SAS
SENS 1
SENS 0
SIGNALLING
ALEN
LED
WARN
ALARM
COSC
MODE
SYNC
March 2001
Page 2 of 15
High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
Pin Description
AS8413
Pin #
Name
Description
1
TX1
40-kHz burst generator - output 1.
2
OSCIN
Clock input or crystal / ceramic resonator connection.
3
OSCOUT
Crystal / ceramic resonator connection. Not connected when external clock is applied.
4
COSC
Clock output to slave IC
5
VCAP
Pin for programming capacitor at the envelope detector.
6
AVDD
Analog supply voltage (+5V).
7
AGND
Analog ground.
8
RXGND
Analog ground.
9
RX
Ultrasonic echo input.
10
SEL40K
Time reference select input (SEL40K=’1’ to select 40 kHz or SEL 40K=’0’ to select
400 kHz at OSCIN).
11
ALEN
Alarm enable input (when ALEN =’0’, the outputs ALARM, WARN and LED are disabled).
12
MODE
Master/slave configuration pin (MODE=’0’ to configure slave IC, MODE=’1’ To configure master IC with delayed sync and MODE open, to configure master IC without
delayed sync)
13
SENS0
Sensitivity selection (least significant bit).
14
SENS1
Sensitivity selection (most significant bit).
15
SAS
SAS enable input (SAS=’1’ activates Self-Adjusting Sensitivity, SAS=’0’ keeps sensitivity fixed)
16
N.C.
(not connected)
17
TP
18
VDD
Test / reset pin. A rising edge resets the IC. This pin should be left unconnected or
tied to VDD for normal operation.
Digital supply voltage (+5V).
19
GND
Digital ground
20
SYNC
Synchronization pin. This pin is configured as output if pin MODE=’1^’ and as input if
MODE=’0’.
21
LED
Active-low signalling LED output (open drain).
22
WARN
Active-low auxiliary alarm output (open drain).
23
ALARM
Active-low main alarm output (open drain).
24
TX2
40-kHz burst generator - output 2.
TX2
ALARM
WARN
Pinout & Packaging
LED
SYNC
Change pinout according to
Pin Description.
GND
VDD
TP
N.C.
Available Package(s):
• 24 pin SOIC
• (24 pin Skinny DIP)
March 2001
SAS
SENS1
SENS0
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High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
Absolute Maximum Ratings
Conditions:
1. AII voltages referenced to GND
2. AVDD connected to VDD
3. AGND connected to GND
Supply Voltage
< 7V
Input Pin Voltage
-0,3 V to VDD + 0.3 V
Output Pin Voltage
-0,3 V to VDD + 0.3 V
Power dissipation
500 mW
Operating temperature under bias
-40 °C to +85 °C
Storage Temperature
-65 °C to +150 °C
Latch-up immunity
-10mA … + 10mA
Note:
Stresses above these values may cause permanent damage to the device.
Functional operational at these values is not implied
ESD immunity / HBM; 1500 Ohm; 100 pF
Recommended Operating Conditions
Parameter
Symbol
Min
Typ
Max
Units
Supply Voltage (VDD, AVDD)
VDD
4.5
5.0
5.5
V
Operating Temperature Range
TO
-40
-
85
°C
Clock Frequency (SEL40K=1)
FCK
39
40
41
kHz
AC Peak Voltage at RX Input
VIN
0.1
-
10
mV
D.C. Electrical Characteristics
(VDD = 5 V, VSS = Ground, TA = -40 °C to +85 °C)
Parameter
Symbol
Min
Typ
Max
Units
Low Level Input Voltage
Vil
-
-
1.5
V
Pins 2, 10, 13, 14, 15, 20
High Level Input Voltage
Vih
3.5
-
-
V
Pins 2, 10, 13, 14, 15, 20
Low Level Input Voltage
Vil
-
-
0.5
V
Pin 12
High Level Input Voltage
Vih
4.5
-
-
V
Pin 12
Low-to-High Threshold
Vt+
-
3.0
3.5
V
Pin 11 (Schmitt Trigger Input)
High-to-Low Threshold
Vt-
1.4
1.8
-
V
Pin 11 (Schmitt Trigger Input)
Hysteresis
Vh
0.6
-
-
V
Pin 11
Low Level Input Current
Iil
-1
-
-
µA
Pins 10, 11, 13, 14, 15 (VDD=5 V)
High Level Input Current
Iih
-
-
1
µA
Pins 10,11, 13, 14, 15 (VDD=5V)
Input Resistance
Rin
-
200
-
kΩ
Pin 9
March 2001
Conditions
Page 4 of 15
High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
Low Level Output Voltage
Vol
High Level Output Voltage Voh
Low Level Output Voltage
High Level Output Voltage
-
0.5
V
Pins 1, 20, 24
Iol=3 mA
-
0.5
V
Pins 22,23
Iol=4 mA
-
0.5
V
Pins 21
Iol=12mA
-
V
Pins 1, 20, 24
Ioh=-3 mA
4.0
Vol
Voh
-
-
0.4
V
Pin 4 (SEL40K= 0)
Iol =100uA
-
-
1.5
V
Pin 4 (SEL40K= 1)
Iol =10 uA
4.6
-
-
V
Pin 4 (SEL40K= 0)
Ioh=-100 uA
3.5
-
-
V
Pin 4 (SEL40K= 1)
Ioh=-10 uA
High-Z Output Current
Ioz
-
-
10
µA
Pins 21, 22, 23
Vo=5V
Total Supply Current
Idd
-
0.65
1.0
mA
SEL40K= 1
crystal or clock
-
1.0
1.6
mA
SEL40K= 0
ceramic res onator
C1=C2=100pF
A.C. Electrical Characteristics
(VDD = 5 V, VSS = Ground, TA = 25°C)
Parameter
Power-on-reset width
Self-test delay (incl. tpor )
Symbol
Min
Typ
Max
tpor
50
-
70
500
-
530
500
-
800
1.3
-
1.4
1.7
-
1.9
SEL40K= 1, clock
1.7
-
2.1
SEL40K= 1, crystal
tstd
Units
Conditions
SEL40K= 0, resonator / clock
ms
SEL40K= 1, clock
SEL40K= 1, crystal
s
SEL40K= 0, resonator / clock
Fault indication pulse width
tstw
4.3
-
4.6
s
SYNC pulse width
tsync
-
0.6
-
ms
SYNC period
Tsync
-
44.4
-
ms
ALARM low pulse width
tal
200
-
-
ms
Pins 22, 23
LED low pulse width
tonn
-
89
-
ms
narrow = no detection
tonw
-
977
-
ms
wide = detection
toff
-
888
-
ms
LED low pulse width
System Description
Ultrasonic intrusion detectors are very popular in vehicle security systems, due to their low cost,
good area coverage and easiness of installation. The AS8413 uses the sonar principle to build a
high-performance intrusion detector that follows the requirements of the OEM automotive industry. Additionally, the IC supports the use of two or more pairs of sensors. As very short ultrasonic
bursts are sent, the power needed to drive the transmitter is reduced. Interference and signal
ancellation effects, present in systems with continuous transmission, are virtually eliminated.
March 2001
Page 5 of 15
High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
Fig. 1 shows the pulse/echo timing generated by the AS8413. The basic concept behind the
AS8413 is the detection of changes in the relative position of objects in side the vehicle, by
monitoring successive echo patterns with a discriminator based on fuzzy-logic.
Despite the higher complexity of this approach, that demands both analog and digital signal
processing, the solution is made cost-effective with the use of a single IC and a small number of
external components
0,6ms
TX pulse
44,4ms
Echo in RX
Fig. 1 - Pulse/Echo Timing
Supply / Power-On Reset
The AS8413 requires a single 5-volt power supply. Pins for VDD and GND are separated for the
analog and digital circuits, and a 100-n-F 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 17, 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 dutycycle 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
specifications. The IC power consumption increases with higher capacitor values (Idd= 1.0
mA with 100 pF capacitors).
March 2001
Page 6 of 15
High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
Optionally one of the AS8413 ICs used in a system may have its built-in oscillator and generate
clock to the other IC from its COSC output. A driver would be needed, if IC’s are not adjacent.
Master/slave synchronization
The AS8413 is intended to be used in intrusion detector systems where more than one pair of
transducers is used. Each IC is able to control a single transmitter /receiver pair. In multipletransducer systems it is necessary that the bursts generated by each transmitter are synchronized. Otherwise, the echoes may slip over each other and cause undesirable effects, such as
false alarms.
Each AS8413 IC can be programmed to be either a master that generates an external delayed
sync signal or a slave. This signal may come from the master or from an external circuit, such
as a microcontroller. The sync signal received at the slave is delayed by half transmission period
(22.2 ms) to the internal sync signal used by the master, in order to avoid burst superposition as
much as possible.
The AS8413 can be configured to operate under 3 possible conditions, by programming the
MODE input in one of the three possible conditions:
• logic ‘0’: slave (receives delayed sync)
• logic ‘1’: master in a multi-pair system (generates delayed sync)
• open: master in a single-pair system (AS8412 mode)
Ultrasonic Transducers
The AS8413 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 covered.
In most applications, just two pairs of sensors will be used. The sensors will typically be positioned at the B-pillars (central pillars), close to the roof, to provide the best possible coverage of
all the vehicle interior. Each pillar may have either a transmitter/receiver pair or two sensors of
the same kind. The first arrangement is recommended, as it allows a single box at each pillar
containing the AS8413 and the transducer pair controlled by it, thus decreasing cabling.
The outputs TX1 and TX2 drive the transmitter in a push-pull configuration with 10 V peak-topeak. As shown in Fig. 1, the transmission duty-cycle is very short (around 1/75), reducing the
average current needed to generate the ultrasonic bursts to about 0.05 mA per IC.
Shielded cable is mandatory for the receiver and recommended for the transmitter, unless they
are adjacent to the IC. The shield at the receiver cable must be grounded and connected to the
RXGND pin.
March 2001
Page 7 of 15
High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
Analog Conditioning
The analog front-end, composed of a preamplifier and a filter centered at 40 kHz, increases the
signal level and removes noise outside the bandpass. It is followed by a digitally-controlled AGC
amplifier, that keeps signal level at the VCAP output within prescribed levels. Finally, an envelope
detector extracts the information embedded in the amplified echo signal.
The front-end needs proper bias during power-up. That can be provided by an RC series circuit
to VDD, as shown at Fig. 2, or alternatively, by the pre-amplifier of Fig. 4.
VDD
100n
100k
To RX-Pin
Fig. 2 - Series-RC circuit at RX
The AS8413 has a wide dynamic range, to follow the signal fluctuations that occur in a large
variety of vehicles, sensors and environmental conditions. Only under extreme conditions, like in
a larger vehicle, an external pre-amplifier at RX may help to improve performance.
A practical way to verify if a pre-amplifier might be useful, is by monitoring the echo waveform at
VCAP. For measuring that voltage a FET-input buffer (input impedance at least 109 ohm) should
be used, as the output impedance at VCAP is very high.
A pre-amplifier that satisfies the bias requirements is shown at the Fig. 4. Its gain is around 8 dB.
VCAP(V)
3,0V-4,2V
1,3V-1,8V
0
10
20
30
40
T(ms)
Period = 44,4 ms
Fig. 3 - Waveform at VCAP
March 2001
Page 8 of 15
High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
Fig. 4 - Recommended pre-amplifier
As a general rule, the best approach is to measure the voltage at the “valley”, that normally occurs at the end of the echo waveform. If it is above 1.8 V, then the system could benefit from
some extra gain.
Sensitivity Programming
The AS8413 allows the sensitivity to intrusions and movements to be programmed at production, so the manufacturer can adapt the detector to different requirements.
There are two possible ways of programming the sensitivity:
• Digital programming by the pins SENS1 and SENS0: controls the criteria used by the discriminator to validate intrusions or movements. Four sensitivities are available, as shown at
Table 1.
Table 1. Digital programmable sensitivities
SENS1
SENS0
1
1
Sensitivity
High
1
0
Mid-high
0
1
Mid-low
0
0
Low
• Capacitor at the pin VCAP: controls the analog processing of the echo signal at the envelope
detector. With smaller capacitors, the digitized echo signal will have a higher resolution and,
as a result, a higher sensitivity will be obtained.
The best combination of digital programming and VCAP capacitor is usually determined by
experiment. A generally good choice is to use sensitivity mid-high with a 270-pF capacitor at
VCAP.
March 2001
Page 9 of 15
High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
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 sensitivity 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
MID-HIGH
MID-LOW
LOW
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.
March 2001
Page 10 of 15
High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
• SAS disabled (pin SAS = “0”)
The IC will keep the sensitivity fixed at the upper limit of the programmed range, regardless of
the environmental conditions. This mode can be useful in special applications that demand a
fixed or externally controlled sensitivity. The VCAP capacitor may have to be up to 4 times
bigger than it would be with the SAS enabled, to compensate the fixed high sensitivity and
avoid false alarms. Another use of this mode is to allow an easier characterization of the upper sensitivity limit during the system development.
The self-test indicates an error with SAS = ”0”. To generate a valid self-test, SAS must be “1”
during power-up. It may be switched afterwards.
Together with the AGC, the SAS loop provides improved controllability over the intrusion detection process, allowing the system to be little affected by changes in the external conditions, such
as temperature, supply voltage and sensitivity of the ultrasonic sensors.
In any case, the sensitivity can be very significant, so the AS8413 is not adequate to be used in
convertibles or with open windows.
DSP and Fuzzy-Logic Discriminator
Many external phenomena may affect the ultrasonic waves inside the vehicle. Sunlight, blows at
the glasses or roof, wind through the ventilation flaps are some examples.
Experiments have shown that a real intrusion can not be validated by a single specific characteristic of the echo waveform. Several parameters must be observed at the same time and also
how they correlate with each other. Experimental data gathered from extensive field testing were
used to support the detection criteria embedded in the AS8413.
To implement those criteria, first the digitized echoes are processed by a DSP circuit to enhance the parameters to be monitored. Then, a fuzzy-logic discriminator continuously examines
how those parameters change and correlate, to verify any possible intrusion.
Built-In-Self-Test
When power is applied and SAS=’1’, the master AS8413 goes automatically into a self-test routine that checks the IC operation. It can also detect initialization errors due to a slow supply rise
time or a clock problem at OSCIN. The self-test does not operate in a slave IC.
During the self-test period, the IC outputs are exercised and should be ignored. If the test is successful, normal operation starts, indicated by the output LED pulsing periodically.
In the case of an IC malfunction, immediately after the self-test the LED and WARN outputs are
turned on (low) for about 4.4 seconds. If a light-emitting diode is connected to the LED output,
the self-test message may be seen directly by the user.
After an error message, the LED starts to blink again, as in a normal operation. Fig. 6 shows the
possible self-test waveforms after power-on.
March 2001
Page 11 of 15
High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
VDD
t
s td
WARN DON’T CARE
DON’T CARE
t
t
off
o n n
(a)
VDD
t
std
t
stw
WARN DON’T CARE
DON’T CARE
t
o ff
t
o n n
(b)
Fig. 6
(a) Self-Test OK
(b) Error at Self-Test
Alarm Signalling
The AS8413 can indicate not only intrusion or motion, but also other kinds of disturbance, and
send a particular message for each situation. Those disturbances are defined as follows and the
messages are identified at Table 3.
• Weak intrusion: early stages of an intrusion, or a weaker intrusion or movement. Detection
criteria are similar to those for intrusion, but with higher sensitivity.
• Blockage: elimination of the coupling between the transducers, either by blocking one of
them, or by cutting a wire.
• Saturation: very strong 40-kHz signal at RX, possibly an attempt to sabotage the alarm system by saturating the receiver. May also be caused by a glass breakage or by strong hits with
hard objects at the glass.
With this signalling scheme, the IC has flexibility to be used either in simpler applications or in
sophisticated microprocessor based systems. In addition, the manufacturer has the option to
choose which kind of disturbance should be an alarm condition.
The pulse widths are those specified in the AC electrical Characteristics and shown in Fig. 7. At
ALARM and WARN they are at least 200ms; the outputs remain active if intrusion or motion persists.
The WARN output could be used instead of the ALARM, if only intrusion detections should be
flagged. In this case, the digital sensitivity should be scaled one step ower (for instance from
mid-high to mid-low), or the capacitor at VCAP increased, to keep approximately the same sensitivity.
March 2001
Page 12 of 15
High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
The blockage and saturation are signalized just one time at each occurrence, to avoid continuous alarm triggering. Detection of glass breakage by saturation is not guaranteed.
Table 3. Disturbances detected by the AS8413
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
t al
t al
WARN
t al
ALARM
t ONW
tONN
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 indicates
the test result.
By grounding ALEN, the IC can be made inoperative as seen by the control unit and still keep 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 indication may occur, due to thermal gradients inside the vehicle. That sould be considered when
choosing a courtesy time for a AS8413-based system. When a 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
March 2001
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High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
Application Circuit
A typical Application Circuit for the AS8413 is presented at Fig. 8, where a 400 kHz oscillator with
external ceramic resonator is built for each IC. This circuit is suitable to be used in a microcontroller-based alarm system.
Optionally, the microcontroller could synthesize a 40 kHz for the ICs, decreasing component
count and power at the system level. The digital sensitivity also can be controlled, in specific
applications.
If access to all the signalling outputs of both ICs is provided, the alarm system will be able to
identify the kind of disturbance detected and the region where it occurred.
VDD
TXM
Res.
400kHz
1
2
100 p
3
4
100p
5
270p
VDD
6
7
100n
8
9
RX M
VDD
10
11
12
TX2
TX1
OSCIN
OSCOUT
ALARM
WARN
COSC
LED
VCAP
SYNC
AVDD
GND
AGND
VDD
TP
RXGND
RX
N.C.
SEL4OK
SAS
ALEN
SENS1
MODE
SENS0
24
56k
23
22
21
VDD
330
20
19
18
100n
VDD
17
16
15
VDD
14
13
(MASTER)
VDD
TXS
Res.
400kHz
1
2
100 p
3
4
100p
270p
5
VDD
100n
6
7
8
9
RX S
VDD
10
11
12
TX2
TX1
OSCIN
OSCOUT
ALARM
WARN
COSC
LED
VCAP
SYNC
AVDD
GND
AGND
VDD
TP
RXGND
RX
N.C.
SEL4OK
SAS
ALEN
SENS1
MODE
SENS0
24
56k
23
22
21
VDD
330
20
19
18
100n
VDD
17
16
VDD
15
14
13
(SLAVE)
Fig. 8 - Application Circuit
March 2001
Page 14 of 15
High Performance Automotive Sonar Intrusion – Data Sheet
AS8413
EMI Protection
The usual precautions against EMI, such as PCB with ground plane, short tracks and shielded
cables, are recommended for AS8413 applications, to avoid possible effects from noise induced
by external sources.
The RX cable must be shielded, because of the low-voltage signal. An alternative to protect other
pins directly connected to unshielded cables, is to clamp induced voltages with signal diodes
close to the pins (Fig.9)
If a single shielded cable is used for the transmitting sensor, the internal wire may be connected
to TX1 and the shield connected to TX2. In this case, only the TX2 output will need protection
diodes
VDD
IC
IC
(a)
(b)
Fig. 9 - Diode Clamp Protection for
Unshielded Cables
(a) pins 1, 24
(b) pins 21, 22, 23
Copyright  2000, Austria Mikro Systeme International AG, Schloß Premstätten, 8141 Unterpremstätten, Austria.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by
any means, without the prior permission in writing by the copyright holder. To the best of its knowledge, Austria Mikro Systeme
International asserts that the information contained in this publication is accurate and correct.
March 2001
Page 15 of 15
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