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PDF TDA7476 Data sheet ( Hoja de datos )
| Número de pieza | TDA7476 | |
| Descripción | CAR RADIO DIAGNOSTIC PROCESSOR | |
| Fabricantes | ST Microelectronics | |
| Logotipo |  |
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® TDA7476
CAR RADIO DIAGNOSTIC PROCESSOR
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 VS
- audio channel shorted to GND
- aux input shorted to GND
NOISE FREE DIAGNOSTICS OPERATION
PROTETCTORS
LOAD DUMP VOLTAGE
PRELIMINARY DATA
MULTIPOWER BCD TECHNOLOGY
SO24
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 (I2C
bus compatible) in order to disable the ICs under
fault and/or to alert µcontroller by means of warn-
ing messages.
PIN CONNECTION (Top view)
GND
SDA
SCL
ADD
W
AUX1 OUT
AUX1 IN
AUX2 IN
AUX2 OUT
5V
ST-BY
VS
1 24
2 23
3 22
4 21
5 20
6 19
7 18
8 17
9 16
10 15
11 14
12 13
D97AU570
CH5-
CH5+
CH4+
CH4-
CH3-
CH3+
CH2+
CH2-
CH1-
CH1+
T-CAP
CURR. SET. RES.
December 1999
1/15
This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
1 page  
TDA7476
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. (RL = Vthr*/Isink).
S.C. across Load x Normal Operation x Open Load
Rcs = 3.3kΩ 0Ω
0.5Ω 2Ω
20Ω 50Ω
infinite
S.C. across Load x Normal Operation x Open Load
Rcs = 1.8kΩ
0Ω
0.27Ω 1.1Ω
11Ω 27Ω
infinite
D96AU500
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 tm is high and the outputs of the amplifiers are able to rise
over 1V;
- a resistor RCS 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 (RL = Vthr/Isource)
Rcs = 4.7kΩ S.C. across Load x Normal Operation x
Open Load
0Ω
0.47Ω 1.9Ω
19Ω 47Ω
infinite
Rcs = 2.7kΩ S.C. across Load x Normal Operation x
Open Load
0Ω
0.27Ω 1.1Ω
11Ω 27Ω
infinite
D96AU501
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.
(*) 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..)
5/15
5 Page 
TDA7476
READ BYTE 1
MSB
LSB
D7 D6 D5 D4 D3 D2 D1 D0
STATUS
0 0 X X 1 1 X 0 CH1 short circuit to Vs
0 0 X X 1 1 0 X CH1 short circuit to GND
0 0XX1 11 1
0 0XX1 11 1
0 0 X 0 1 1 X X CH2 short circuit to Vs
0 0 0 X 1 1 X X CH2 short circuit to GND
0 01 11 1XX
0 01 11 1XX
READ BYTE 2
1 1 X X 1 1 X 0 CH3 short circuit to Vs
1 1 X X 1 1 0 X CH3 short circuit to GND
1 1XX1 11 1
1 1XX1 11 1
1 1 X 0 1 1 X X CH4 short circuit to Vs
1 1 0 X 1 1 X X CH4 short circuit to GND
1 11 11 1XX
1 11 11 1XX
READ BYTE 3
1 1 X X X X 1 0 AUX1 short circuit to GND
1 1 X X X X 0 1 AUX1 open load
1 1 X X 1 0 X X AUX2 short circuit to GND
1 1 X X 0 1 X X AUX2 open load
1 1 X 0 X X X X CH5 short circuit to Vs
1 1 0 X X X X X CH5 short circuit to GND
1 1 1 1XXXX
1 1 1 1XXXX
Repetitive turn-on diagnostic
During the turn-on diagnostic, the TDA7476 can reveal false ”short circuit across load” and/or false ”open
load” due to noise sources such as door slams.
This problem can be solved doing more than one turn-on diagnostic routine. If the µP asks for N times
the state of the audio system, it has to consider a fault as really present only if it is detected in all the N
turn-on diagnostic.
As above explained, the first time the TDA7476 receivers the byte ADD1, it does the turn-on diagnostic;
then each timeit is addessed with ADD1, it does the permanent diagnostic. This is not true if, when the
µP sends for the forst time the byte ADD2, it does not send to the TDA7476 the acknowledge after it has
received the byte BYTE3. In this case, the TDA7476 does not switch from turn-on to permanent diagnos-
tic mode so if it receives again the byte ADD1 it works as it was the first time that it does the turn-on di-
agnostic. In order to do repetitive turn-on diagnostic, the µP has to be programmed as following:
Step 1: the µP sends ADD1
START
ADD1
ACK
STOP
Step 2: the µP waits Twait1 seconds
Step 3: the µP sends ADD2, receives BYTE1, BYTE2, BYTE3, does not send the acknowlegde af-
ter BYTE3
START
ADD2
ACK
BYTE1
ACK
BYTE2
ACK
BYTE3
STOP
Step 4: repeat Step1, Step2, Step3 while the second, third, fourth, ...turn-on diagnostic has to be
done.
During the last turn-on diagnostic the µP sends ADD2, receives BYTE1, BYTE2, BYTE3, and
sends the acknowlegde after BYTE3
START ADD2
ACK
BYTE1
ACK
BYTE2
ACK
BYTE3
ACK
STOP
11/15
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet TDA7476.PDF ] | |
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