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TDA7476
CAR RADIO DIAGNOSTIC PROCESSOR
PRELIMINARY DATA
WIDE OPERATING VOLTAGE RANGE
ST-BY FUNCTION (C-MOS)
LOW QUIESCENT ST-BY CURRENT CON-
SUMPTION
I2C BUS INTERFACE WITH 2 EXTERNALLY
SELECTABLE ADDRESSES
UP TO 5 BTL EQUIVALENT INPUTS FOR
FAULT DETECTION IN THE AUDIO CHAN-
NELS
- short to GND
- short to Vs
- short across the load (at turn-on)
- open load (at turn-on)
2 AUX INPUTS FOR FAULT DETECTION IN
THE ANTENNA AND BOOSTERS SUPPLY
LINE
- short to GND
- open load
WARNING PIN FUNCTION (interrupt facility)
ACTIVATED IN THE FOLLOWING CONDI-
TION:
- audio channel shorted to V
S
- audio channel shorted to GND
- aux input shorted to GND
NOISE FREE DIAGNOSTICS OPERATION
PROTETCTORS
LOAD DUMP VOLTAGE
OPEN GND
REVERSED BATTERY
ESD
DESCRIPTION
The car radio diagnostic processor is an interface
chip in BCD Technology intended for car radio
applications. It is able to detect potential faults
coming from any misconnection in the car radio or
in the harness when installing the set.
The device is able to reveal any fault in the loud-
speaker lines and in the antenna and booster
supply lines, providing a proper output signal (I
2
C
bus compatible) in order to disable the ICs under
fault and/or to alert
controller by means of warn-
ing messages.
This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
December 1999
GND
SDA
SCL
ADD
W
AUX1 IN
AUX1 OUT
AUX2 IN
AUX2 OUT
CH1-
CH2-
CH2+
CH3-
CH3+
CH4-
CH4+
CH5+
CH5-
1
3
2
4
5
6
7
8
9
22
21
20
19
18
16
17
15
23
10
24
5V
CH1+
D97AU570
ST-BY
T-CAP
11
14
13
12
V
S
CURR. SET. RES.
PIN CONNECTION (Top view)
SO24
MULTIPOWER BCD TECHNOLOGY
1/15
I
2
C
INTERFACE
ADD
DIG-GND
SCL
SDA
AUX1
AUX2
RSENS1
RSENS2
D96AU499A
CH5
CH4
CH3
CH2
CH1
CURRENT
FORCING
&
COMPARATORS
DELAY
VOLTAGE REGULATOR
&
TEST SIGNAL GENERATOR
OUT
IN
IN
OUT
R
CS
C
T
W
ST-BY
SW1
C2
100nF
5V
REF
V
S
12
2
3
4
5
11
10
14
13
1
9
8
7
6
15
16
17
18
19
20
21
22
23
24
C3
10
F
R3
10K
R4
10K
R5 51
C1
10
F
BLOCK DIAGRAM
THERMAL DATA
Symbol
Parameter
Value
Unit
R
Th j-amb
Thermal resistance junction to ambient
Max.
85
C/W
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Value
Unit
V
op
Operating Supply Voltage
18
V
V
s
DC Supply Voltage
28
V
V
peak
Peak Supply Voltage t = 50ms
40
V
P
tot
Total Power Dissipation Tcase = 25
C
1.5
W
T
stg
; T
j
Storage and Junction Temperature
-40 to 150
C
V
SB
Stand-by Pin Voltage
6
V
V
SDA
SDA Pin Voltage
6
V
V
SCL
SCL Pin Voltage
6
V
V
ADD
ADD Pin Voltage
6
V
ELECTRICAL CHARACTERISTICS (V
s
= 14.4V; T
amb
= 25
; R
L
= 4
, unless otherwise specified.)
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
V
SB
IN
Stand-By IN Threshold
1.5
V
V
SB
OUT
Stand-By OUT Threshold
3.5
V
I
SB
Stand-By Current Consumption
Stand-By Voltage Pin = 1.5V
100
A
Iq
Total Quiescent Current
Total quiescent Current with
TDA7476 not addressed
5
mA
TDA7476
2/15
ELECTRICAL CHARACTERISTICS (continued)
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
AUDIO INPUTS CH1, CH2, CH3, CH4, CH5 - TURN ON DIAGNOSTIC
Pgnd
Short to GND det. (below this
limit, the Audio Output is
considerd in Short Circuit to
GND)
Power amplifier in st-by
condition
0.8
V
Pvs
Short to Vs det. (above this
limit, the Audio Output is
considered in Short Circuit to Vs)
Vs-0.7
V
Pnop
Normal operation thresholds.
(Within these limits, the Audio
Output is considered without
faults)
1.2
Vs-1.3
V
Lsc
Shorted Load det. (voltage
across the Audio Outputs).
Below this limit the load is
considered shorted.
5
mV
Lop
Open Load det. (voltage across
the Audio Outputs). Above this
limit the load is considered open.
550
mV
Lnop
Normal load det. (Voltage
across the Audio Output).
Within these limits the load
resistance is considered normal.
22
220
mV
AUX INPUTS AUX1, AUX2 - TURN ON DIAGNOSTIC
Agnd
Short to GND det. (voltage
across the sensing resistor).
Above this limit the AUX pin is
considered in Short Circuit to
GND.
High side driver ON
0.75
V
Aol
Open load det. (voltage across
the sensing resistor). Below this
limit the Aux pin is considered in
Open Load condition.
0.085
V
Anop
Normal Operation det. (Voltage
across the sensing resistor).
Within these limits the load
resistance connected to the Aux
pin is considered correct.
0.125
0.5
V
AUDIO INPUTS - PERMANENT DIAGNOSTIC
Pgnd
Short to GND det. (below this
limit, the Audio Output is
considered in Short Circuit to
Vs) This condition must be true
for a time higher than Tdel
Power amplifier ON
0.8
V
Pvs
Short to Vs det. (above this limit
the Audio Output is considered
in Short Circuit to Vs) This
condition must be true for a time
higher than Tdel
Vs-0.7
V
Pnop
Normal operation thresholds.
(Within these limits, the Audio
Output is considered without
faults)
1.2
Vs-1.3
V
TDA7476
3/15
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
AUX INPUTS - PERMANENT DIAGNOSTIC
Agnd
Short to GND det. (above this
limit, the Audio Output is
considered in Short Circuit to
Vs) This condition must be true
for a time higher than Tdel
High side driver ON
0.75
V
Aol
Open load det. (voltage across
the sensing resistor. Below this
limit the Aux pin is considered in
Open Load condition)
This condition must be true for a
time higher than Tdel
0.085
V
Anop
Normal Operation det. (Voltage
across the sensing resistor.
Within these limits the load
resistance connected to the Aux
pin is considered correct)
0.125
0.5
V
PERMANENT DIAGNOSTIC - ACQUISITION TIME DELAY
Tdel
Acquisition time delay - The
fault is considered true if the
fault condition are present for
more than Tdel without
interruption
2
s
PERMANENT DIAGNOSTIC - WARNING PIN
Vsat
Saturation voltage on pin 5
Sink Current at Pin 5 = 1mA
1
V
ADDRESS SELECT
V
ADD
Voltage on pin 4
Address 0100010X
1.5
V
Address 0100011X
3
5
V
I
2
C BUS INTERFACE
f
SCL
Clock Frequency
400
KHz
V
IL
Input Low Voltage
1.5
V
V
IH
InputHigh Voltage
3
V
V
SAT
Sat Voltage at pin 2
Sink Current at Pin 2 = 5mA
1.5
V
ELECTRICAL CHARACTERISTICS (continued)
WORKING PRINCIPLES
Turn-on diagnostic - CH1, CH2, CH3, CH4, CH5 - Shorted load/open load detection
To detect a short across the load or an open load, a subsonic current pulse is generated. The infor-
mation related to the status of the outputs are measured and memorized at the top of the current
pulse (tm in fig.1). The current is sourced by the positive pins (CH1+,...CH5+) and it is sunk by the
corresponding negative pins (CH1-,...CH5-).
Isink and Isource are depending on the external resistor Rcs. The minimum allowed value for Rcs is
1.65KOhm. The relationship among Isink, Isource and Rcs is the following:
Isink = (3.3/Rcs) x 11
Isource = 1.5 x Isink
t
m
t
s
t
(ms)
I
SOURCE
I
SINK
I(mA)
D97AU571
Figure 1.
TDA7476
4/15
On bridge (or bridge equivalent) devices if there is no short circuit to GND or to Vs, Isource goes into
saturation mode (for Vout > 3V), and in the load flows Isink. As the turn-on diagnostic thresholds are
fixed, it is possible to calculate the ranges of loudspeaker resistance in which short circuit, normal op-
eration and open load are detected.
For example, here below are two cases, with Rcs = 3.3KOhm and Rcs = 1.8KOhm. (R
L
= Vthr*/Isink).
S.C. across Load
x
Open Load
0
1.1
11
infinite
x
Normal Operation
0.27
27
D96AU500
S.C. across Load
x
Open Load
0
2
20
infinite
x
Normal Operation
0.5
50
The exact values of the above mentioned resistive ranges may vary a little, depending on the power
amplifier used. These values for the various possible ST power amplifiers will be communicated later.
When single-ended devices are used and the application circuit is as shown in fig. 5,6, it is necessary
to use:
- a greater timing capacitor so that the time t
m
is high and the outputs of the amplifiers are able to rise
over 1V;
- a resistor R
CS
1.5 times higher than that used for the bridge amplifiers.
In this case, the loudspeaker resistance ranges in which short circuit, normal operation and open load
are detected will be as follows with Rcs = 4.7KOhm and Rcs = 2.7KOhm (R
L
= Vthr/Isource)
S.C. across Load
x
Open Load
0
1.9
19
infinite
x
Normal Operation
0.47
47
D96AU501
S.C. across Load
x
Open Load
0
1.1
11
infinite
x
Normal Operation
0.27
27
The exact values of the above mentioned resistive ranges may vary a little, depending on the power
amplifier used. These values will be communicated later.
Turn-on diagnostic - CH1, CH2, CH3, CH4, CH5 - Short to GND and Vs.
To detect if there is short circuit to GND or Vs, the subsonic current pulse is exploited. The information
related to the status of the outputs are measured and memorized at the top of the current pulse (tm in
fig.1). If no faults are present, the pins connected to the audio outputs (CH1,..CH5) will reach about 3V.
If one or more outputs are shorted to GND, these voltages become lower than 3V.
If one or more outputs are shorted to Vs, the output voltage increases over 3V.
The fault status can be know by sensing the output voltages. The reason way voltage threshold has
been preferred instead of a current threshold to declare short circuit resistor ranges is two fold:
1) The amplifier can drain current in the resistive path of the short circuit, hence this current and conse-
quently the short circuit resistor cannot be determined with a sufficient level of accuracy.
2) The voltage difference between the car radio ground (reference) and the position of the chassis of the
car where the loudspeaker line is connected (due to an accidental short circuit) can be up to some
hundreds of mV. This does not permit a correct measure of the short circuit resistor.
Rcs = 3.3k
Rcs = 1.8k
Rcs = 4.7k
Rcs = 2.7k
(*) Vthr is the threshold described in the table on page 3/14 - 4/14 (for example Pgnd-min, Pvs - max, Pnop - min, Pnop - max etc..)
TDA7476
5/15
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