STMICROELECTRONICS TDA7476

TDA7476

CAR RADIO DIAGNOSTIC PROCESSOR
PRELIMINARY DATA
WIDE OPERATING VOLTAGE RANGE
ST-BY FUNCTION (C-MOS)
LOW QUIESCENT ST-BY CURRENT CONSUMPTION
I2C BUS INTERFACE WITH 2 EXTERNALLY
SELECTABLE ADDRESSES
UP TO 5 BTL EQUIVALENT INPUTS FOR
FAULT DETECTION IN THE AUDIO CHANNELS
- 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 CONDITION:
- audio channel shorted to VS
- audio channel shorted to GND
- aux input shorted to GND
NOISE FREE DIAGNOSTICS OPERATION
PROTETCTORS
LOAD DUMP VOLTAGE
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 loudspeaker 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 warning messages.
PIN CONNECTION (Top view)
GND
1
24
CH5-
SDA
2
23
CH5+
SCL
3
22
CH4+
ADD
4
21
CH4-
W
5
20
CH3-
AUX1 OUT
6
19
CH3+
AUX1 IN
7
18
CH2+
AUX2 IN
8
17
CH2-
AUX2 OUT
9
16
CH1-
5V
10
15
CH1+
ST-BY
11
14
T-CAP
VS
12
13
CURR. SET. RES.
D97AU570
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.
TDA7476
BLOCK DIAGRAM
2
SDA
24
3
SCL
ADD
23
I2C
4
CH5
INTERFACE
22
21
CH4
12
VS
C3
10µF
R3
10KΩ
20
C2
100nF
19
5
W
CH3
18
DELAY
17
R4
10KΩ
CURRENT
FORCING
&
COMPARATORS
11
ST-BY
SW1
10
14
5V
REF
13
CH2
16
15
CH1
6
VOLTAGE REGULATOR
&
TEST SIGNAL GENERATOR
OUT
RSENS1
AUX1
7
C1
10∝F
CT
IN
RCS
8
IN
RSENS2
R5 51Ω
1
DIG-GND
AUX2
9
OUT
D96AU499A
ABSOLUTE MAXIMUM RATINGS
Symbol
Value
Unit
Vop
Operating Supply Voltage
18
V
Vs
DC Supply Voltage
28
V
Peak Supply Voltage t = 50ms
40
V
Total Power Dissipation Tcase = 25°C
1.5
W
-40 to 150
°C
Vpeak
Ptot
Tstg; Tj
Parameter
Storage and Junction Temperature
VSB
Stand-by Pin Voltage
6
V
VSDA
SDA Pin Voltage
6
V
VSCL
SCL Pin Voltage
6
V
V ADD
ADD Pin Voltage
6
V
THERMAL DATA
Symbol
RTh j-amb
Parameter
Thermal resistance junction to ambient
Max.
Value
Unit
85
°C/W
ELECTRICAL CHARACTERISTICS (Vs = 14.4V; Tamb = 25°; RL = 4Ω, unless otherwise specified.)
Symbol
VSBIN
VSBOUT
2/15
Parameter
Test Condition
Min.
Typ.
Stand-By IN Threshold
Stand-By OUT Threshold
Max.
Unit
1.5
V
100
µA
3.5
ISB
Stand-By Current Consumption
Stand-By Voltage Pin = 1.5V
Iq
Total Quiescent Current
Total quiescent Current with
TDA7476 not addressed
V
5
mA
TDA7476
ELECTRICAL CHARACTERISTICS (continued)
Symbol
Parameter
Test Condition
AUDIO INPUTS CH1, CH2, CH3, CH4, CH5 - TURN ON DIAGNOSTIC
Power amplifier in st-by
Pgnd
Short to GND det. (below this
condition
limit, the Audio Output is
considerd in Short Circuit to
GND)
Pvs
Short to Vs det. (above this
limit, the Audio Output is
considered in Short Circuit to Vs)
Pnop
Normal operation thresholds.
(Within these limits, the Audio
Output is considered without
faults)
Lsc
Shorted Load det. (voltage
across the Audio Outputs).
Below this limit the load is
considered shorted.
Lop
Open Load det. (voltage across
the Audio Outputs). Above this
limit the load is considered open.
Lnop
Normal load det. (Voltage
across the Audio Output).
Within these limits the load
resistance is considered normal.
AUX INPUTS AUX1, AUX2 - TURN ON DIAGNOSTIC
High side driver ON
Agnd
Short to GND det. (voltage
across the sensing resistor).
Above this limit the AUX pin is
considered in Short Circuit to
GND.
Aol
Open load det. (voltage across
the sensing resistor). Below this
limit the Aux pin is considered in
Open Load condition.
Anop
Normal Operation det. (Voltage
across the sensing resistor).
Within these limits the load
resistance connected to the Aux
pin is considered correct.
AUDIO INPUTS - PERMANENT DIAGNOSTIC
Power amplifier ON
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
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
Pnop
Normal operation thresholds.
(Within these limits, the Audio
Output is considered without
faults)
Min.
Typ.
Max.
Unit
0.8
V
Vs-0.7
1.2
V
Vs-1.3
V
5
mV
550
22
mV
220
0.75
0.125
V
0.085
V
0.5
V
0.8
V
Vs-0.7
1.2
mV
V
Vs-1.3
V
3/15
TDA7476
ELECTRICAL CHARACTERISTICS (continued)
Symbol
Parameter
Test Condition
AUX INPUTS - PERMANENT DIAGNOSTIC
High side driver ON
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
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
Anop
Normal Operation det. (Voltage
across the sensing resistor.
Within these limits the load
resistance connected to the Aux
pin is considered correct)
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
PERMANENT DIAGNOSTIC - WARNING PIN
Vsat
Saturation voltage on pin 5
Sink Current at Pin 5 = 1mA
ADDRESS SELECT
VADD
Voltage on pin 4
Address 0100010X
Address 0100011X
I2C BUS INTERFACE
fSCL
Clock Frequency
V IL
Input Low Voltage
VIH
InputHigh Voltage
VSAT
Sat Voltage at pin 2
Sink Current at Pin 2 = 5mA
Min.
Typ.
Max.
0.75
V
0.125
0.085
V
0.5
V
2
3
Unit
s
1
V
1.5
5
V
V
400
1.5
KHz
V
V
V
3
1.5
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 information 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-).
Figure 1.
I(mA)
I SOURCE
ISINK
tm
D97AU571
ts
t (ms)
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
4/15
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 operation 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
Rcs = 3.3kΩ
0Ω
x
Normal Operation
0.5Ω
2Ω
S.C. across Load
x
x
20Ω
Normal Operation
Open Load
50Ω
x
infinite
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 t m 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
0Ω
Rcs = 2.7kΩ
0.47Ω
S.C. across Load
0Ω
x
0.27Ω
Normal Operation
1.9Ω
x
19Ω
Normal Operation
1.1Ω
x
11Ω
Open Load
47Ω
x
infinite
Open Load
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 consequently 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
TDA7476
Turn-on diagnostic - AUX1, AUX2
To detect if there is a short circuit to GND or an open load involving to the AUX output of the car radio,
the voltage across a sensing resistor Rsens is detected.
These output voltages (for example for the active antenna and for the booster) are usually generated
by high side drivers, but also voltage regulators with Vout > 5V are admissible.
The detection ranges can be set by adjusting the sensing resistors Rsens1 or Rsens2.
For example, if Rsens = 5Ohm, the following detection table will be operative (I = Vthr/Rsens):
S.C. to GND
x
Normal Operation
150mA 100mA
x
Open Load
25mA 17mA
D96AU503
Permanent diagnostic - CH1, CH2, CH3, CH4, CH5 - Short to GND and Vs
During the CAR-RADIO normal operation, to detect a short circuit to GND (or to Vs), the output voltages are sensed. If one or more outputs stay at any voltage below 0.8V or over Vs-0.8V for more than
2 sec. (typ), the warning pin is pulled down.
The µP can address the TDA7476 to know the status.
The subsonic current pulse is activated also in this case. The fault is correctly detected if it remains
until the memorization (tm in fig.1).
In this phase, faults regarding shorts across the load and open loads cannot be detected.
For single-ended devices as in fig. 5, 6 a short citcuit to ground is detected both when a short to
ground is really present and when the load is missing.
Permanent diagnostic - AUX1, AUX2 - Short circuit to GND and open load
The detection mode of the auxiliary inputs is equal to what is in place during turn-on, but the fault
must be lasting without interruption for more than 2 seconds.
The warning pin is pulled down only in case of short to GND. This is to avoid that this pin remains permanently to 0 level if one or both AUX outputs of the car radio are unused.
Timing
From the byte ”ADD1” to the byte ”ADD2” the µP must wait a period Twait1(see Software Specification) that is depending on the timing capacitor CT according to the following table (Twait1> tm, max):
CT (µF)
tm max (ms)
3.3
45
4.7
65
10
130
22
290
47
620
100
1300
Note: any (positive) spread of the capacitor value must be added. The relation to be used to determine
Twait1 from the value of CT according to the following:
Twait1 > tm, max = (130 x CT/10µF)ms
After the byte ”ADD2” the power amplifier can be switched-on. In some cases, the µP has to wait until
the current pulse is finished (Twait2). This time (ts in fig.1) is given by:
Twait2 > ts, max = (140 x CT/10µF)ms
For bridge or bridge equivalent devices (figg.7,8), Cs = 10µF will be enough.
For the TDA7375, connected as in fig.5, Cs = 47µF if Cout = 1000µF, and Cs = 100µF if Cout = 2200µF.
If the circuit is as shown by fig. 6, the suggested values of Cs are as follows: Cs = 22µF if Cout =
1000µF, Cs = 47µF if Cout = 2200µF.
6/15
TDA7476
TURN-ON DIAGNOSTIC - THRESHOLDS
CH1, CH2, CH3, CH4, CH5
Output voltage during test. (The power amplifier must be in ST-BY mode).
S.C. to GND
0V
x
Normal Operation
0.8V
1.2V
x
VS-1.3
S.C. to Vs
VS-0.7V
D96AU502A
VS
Voltage across the load during test. (The power amplifier must be in ST-BY mode).
S.C. across Load
0V
x
5mV
Normal Operation
22mV
x
220mV
Open Load
550mV
D97AU631A
VS
Note: some faults can mask others if they are present at the same moment on the same channel:
- If there is a short to GND and an open load on the same channel, the TDA7476 gives information
only about one of them, depending on the wire on which the short circuit is present.
- The short circuit to GND masks any short circuit across the load.
- The short circuit to Vs masks any short or open load.
AUX1 - AUX2
Voltage across the sensing resistors.
S.C. to GND
VS
x
0.75V
Normal Operation
0.5V
Open Load
x
125mV
85mV
0V
D97AU572
The minimum voltage of the AUX IN pin to sense the open load condition is 2V.
The minimum voltage of the AUX IN pin to detect the short circuit to GND, by sensing the drop on the
resistors is 4.5V. If this voltage falls below 2V, the AUX in is considered short circuited to GND. From
2V to 4.5V the sensing circuit can detect a short circuit in both ways (by sensing across the resistor or
through the voltage between the AUX IN pin and GND).
PERMANENT DIAGNOSTIC - THRESHOLDS
CH1, CH2, CH3, CH4, CH5
The circuit will recognize as a fault condition any situation where the following short circuit voltages
last more than 2 sec (typ).
Output voltage
S.C. to GND
0V
x
0.8V
Normal Operation
1.2V
x
VS-1.3
S.C. to Vs
VS-0.7V
D97AU573A
VS
AUX1 - AUX2
The voltage across the resistors Rsens1 or Rsens2 is sensed. The circuit will recognize as a fault condition any situation where the following voltages last more than 2sec (typ) in the region ”S.C.to GND”
or ”open load”.
S.C. to GND
VS
0.75V
x
Normal Operation
0.5V
125mV
x
Open Load
85mV
0V
D97AU574
The minimum voltage of the AUX IN pins to sense the open load condition is 2V.
The minimum voltage of the AUX IN pin to detect the short circuit to GND by sensing drop on the resistor is 4.5V. If this voltage is below 2V, the AUX line is considered short circuited to GND. From 2V
to 4.5V the sensing circuit can detect a short circuit in both ways (by sensing across the resistor or
through the voltage between the AUX IN pin and GND).
7/15
TDA7476
I2C BUS INTERFACE
Data transmission from microprocessor to the
TDA7476 and viceversa takes place through the
2 wires I2C BUS interface, consisting of the two
lines SDA and SCL (pull-up resistors to positive
supply voltage must be connected).
Data Validity
As shown by fig. 2, the data on the SDA line must
be stable during the high period of the clock. The
HIGH and LOW state of the data line can only
change when the clock signal on the SCL line is
LOW.
Start and Stop Conditions
As shown by fig. 3 a start condition is a HIGH to
LOW transition of the SDA line while SCL is
HIGH. The stop condition is a LOW to HIGH transition of the SDA line while SCL is HIGH.
Figure 2: Data Validity on the I2CBUS
Figure 3: Timing Diagram on the I2CBUS
Figure 4: Acknowledge on the I2CBUS
8/15
Byte Format
Every byte transferred to the SDA line must contain 8 bits. Each byte must be followed by an acknowledge bit. The MSB is transferred first.
Acknowledge
The transmitter* puts a resistive HIGH level on the
SDA line during the acknowledge clock pulse (see
fig.4). The receiver** the acknowledges has to pulldown (LOW) the SDA line during the acknowledge
clock pulse, so that the SDAline is stable LOW during this clock pulse.
* Transmitter
= master (µP) when it writes an address to
the TDA7476
= slave (TDA7476) when the µP reads a
data byte from TDA7476
** Receiver
= slave (TDA7476) when the µP writes an
address to the TDA7476
= master (µP) when it reads a data byte from
TDA7476
TDA7476
SOFTWARE SPECIFICATIONS
The TDA7476 is activated by turning-on the ST-BY pin (CMOS compatible). In this condition it waits for
the I2CBus addressing byte ADD1 (WRITE to TDA7476)
ADD1
S
010001A
0
ACK
P
This sequence (where the bit 0 of ADD1 is at 0 level) enables the acquisition routine and starts the single
pulse (containing infrasonic harmonics) for the test. During this period the data regarding all the outputs
are memorized.
After a period Twait1 that depends on the value of the timing capacitor (see Timing) the µP redirects the
TDA7476 by the byte ADD2.
ADD2
S
010001A
1
ACK
BYTE 1
ACK
BYTE 2
ACK
BYTE 3
ACK
STOP
The byte ADD2 contains the bit 0 at 1 level. This enables the reading mode, TDA7476’s. The 3 bytes
with the diagnostic information BYTE1, BYTE2, BYTE3 (READ FROM TDA7476) are now transmitted to
the µP.
The address of TDA7476 is selected using pin ADD (pin 4) .
If ADD is connected to ground, then A = 0 and the TDA7476 address is 0100010X.
If ADD is connected to 5V, than A = 1 and the TDA7476 address is 0100011X
The TDA7476 provides two types of diagnostic information:
A) TURN-ON DIAGNOSTIC - The first time that the TDA7476 is addressed by I2CBus, the more complete set of diagnostic information is activated:
- CH1, CH2, CH3, CH4, CH5
Short Circuit to GND
Short Circuit to Vs
Open Load (*)
Short Circuit across the load (*)
(*) Detected if the power amplifiers are in ST-BY condition.
- AUX1, AUX2
Short Circuit to GND (*)
Open Load (*)
(*) Detected if the high side drivers attached to the Aux outputs are ON.
Here following the turn-on diagnostic output bytes
9/15
TDA7476
READ BYTE 1
MSB
D7
X
X
X
X
1
1
1
0
D6
X
X
X
X
1
1
0
1
D5
X
X
X
X
X
0
1
1
D4
X
X
X
X
0
X
1
1
D3
1
1
1
0
X
X
X
X
D2
1
1
0
1
X
X
X
X
D1
X
0
1
1
X
X
X
X
LSB
D0
0
X
1
1
X
X
X
X
CH1 short
CH1 short
CH1 open
CH1 short
CH2 short
CH2 short
CH2 open
CH2 short
circuit to Vs
circuit to GND
load
circuit across the load
circuit to Vs
circuit to GND
load
circuit across the load
X
X
X
X
X
0
1
1
X
X
X
X
0
X
1
1
1
1
1
0
X
X
X
X
1
1
0
1
X
X
X
X
X
0
1
1
X
X
X
X
0
X
1
1
X
X
X
X
CH3 short
CH3 short
CH3 open
CH3 short
CH4 short
CH4 short
CH4 open
CH4 short
circuit to Vs
circuit to GND
load
circuit across the load
circuit to Vs
circuit to GND
load
circuit across the load
X
X
X
X
X
0
1
1
X
X
X
X
0
X
1
1
X
X
1
0
X
X
X
X
X
X
0
1
X
X
X
X
1
0
X
X
X
X
X
X
0
1
X
X
X
X
X
X
AUX1 short circuit to GND
AUX1 open load
AUX2 short circuit to GND
AUX2 open load
CH5 short circuit to Vs
CH5 short circuit to GND
CH5 open load
CH5 short circuit across the load
STATUS
READ BYTE 2
X
X
X
X
1
1
1
0
X
X
X
X
1
1
0
1
READ BYTE 3
X
X
X
X
1
1
1
0
X
X
X
X
1
1
0
1
When the µP reads correctly all the 3 bytes containing the mentioned information and gives the last acknowledge, the TDA7476 switches to the ”permanent diagnostic operation”
B) PERMANENT DIAGNOSTIC
It can sense the following diagnostic information:
CH1, CH2, CH3, CH4, CH5
- Short Circuit to GND
- Short Circuit to Vs
Aux1, Aux2
- Short Circuit to GND (*)
- Open Load (*)
(*) Detected if the high side drivers attached to the Aux outputs are ON.
In this case the above conditions are not detected while the single infrasonic current pulse is present
but before. The fault condition must be present for more than 2sec. (typ) and must be also true during the pulse, where the data are memorized and then transmitted.
The bytes from/to µP and TDA7476 are the same as those in case of turn-on diagnostic (see above).
Here following is the permanent diagnostic output Data Bytes. The bits D7 and D6 of the first byte both
stand at 0 level. This condition, although not possible during the turn-on diagnostic, can be useful to confirm that the bytes are referred to the permanent diagnostic.
10/15
TDA7476
READ BYTE 1
MSB
D7
0
0
0
0
0
0
0
0
D6
0
0
0
0
0
0
0
0
D5
X
X
X
X
X
0
1
1
D4
X
X
X
X
0
X
1
1
D3
1
1
1
1
1
1
1
1
D2
1
1
1
1
1
1
1
1
D1
X
0
1
1
X
X
X
X
LSB
D0
0
X
1
1
X
X
X
X
X
X
X
X
X
0
1
1
X
X
X
X
0
X
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
X
0
1
1
X
X
X
X
0
X
1
1
X
X
X
X
X
X
X
X
X
0
1
1
X
X
X
X
0
X
1
1
X
X
1
0
X
X
X
X
X
X
0
1
X
X
X
X
1
0
X
X
X
X
X
X
0
1
X
X
X
X
X
X
STATUS
CH1 short circuit to Vs
CH1 short circuit to GND
CH2 short circuit to Vs
CH2 short circuit to GND
READ BYTE 2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
CH3 short circuit to Vs
CH3 short circuit to GND
CH4 short circuit to Vs
CH4 short circuit to GND
READ BYTE 3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
AUX1 short circuit to GND
AUX1 open load
AUX2 short circuit to GND
AUX2 open load
CH5 short circuit to Vs
CH5 short circuit to GND
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 diagnostic mode so if it receives again the byte ADD1 it works as it was the first time that it does the turn-on diagnostic. 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 after 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
TDA7476
In this way only after that the TDA7476 has done for N times the turn-on diagnostic, it switches from
turn-on to permanent diagnostic mode.
From now the TDA7476 always does the permanent diagnostic.
To save time when the audio system is switched on, it is possible to do the repetitive turn-on diagnostic
when the car-radio is turned off. In this case the steps to follow to do the repetitive turn-on diagnostic are
the following:
1- to switch off the TDA7476 connecting STBY pin to ground;
2- to wait T5V seconds(time necessaryfor the discharge of the capacitor). If C5V = 10µF then T5V = 20ms typ;
3- to switch on the TDA7476
4- to do the repetitive turn-on diagnostic as above described;
5- to turn off the TDA7476.
WARNING PIN
This is an open drain output pin that is activated when a fault condition is present for more than 2 sec
(TYP). The fault conditions related to the warning pin are as follows:
- AUX1, AUX2
Short to GND
- CH1, CH2, CH3, CH4, CH5:
Short Circuit to GND
Short Circuit to Vs
The purpose of this pin is to alert the µP and start with the permanent diagnostic routine only if faults
are present, thus avoiding CPU’s waste of time.
APPLICATION NOTES
On single-ended devices as in figure 6, 7 if the loads are present then both in turn-on and in permanent diagnostic the fault present on one channel is pointed out for all the loads connected together.
For example:
- see fig.6 if CH1+ is shorted to ground, the TDA7476 reveals a short to groundboth for CH2 and for CH1.
- seefig.7 if CH1+ is shortedto ground, theTDA7476detectsa short circuit to groundfor CH1, CH2, CH3, CH4.
To use the TDA7476 with a car-radio system which has less than five audio channel and less than
two auxiliary loads, it is necessary to take some cares:
- If the loads are 4Ω speakers (Rcs= 3.3 KΩ), R ≅ 10Ω has to be connected between CH+ and CH- of
each channel (see figg. 5,6,7,8 concerning CH5). R ≅ 5Ω has to be used if loads are 2Ω speakers
(Rcs= 1.8 KΩ).
- If AUX1/AUX2 are unused, Rsens1/Rsens2 will not be needed. The AUX-IN pin(s) can be tied to the
5 internal regulator (pin 10) while setting the AUX-OUT pin(s) about 250mV lower than AUX-IN’s
(admissible range = 125mV to 500mV). This can easily be obtained by means of a voltage divider.
If both the AUX channelsare unused, pins 7-8 (AUX-INs) and pins 6-9 (AUX-OUTs) can be respectively
connectedtogether, so that a single voltage divider could be used.
The above actions will prevent any ”warning” activation which might cause unwanted microprocessor’s
interrupt.
12/15
TDA7476
APPLICATION EXAMPLES WITH ST AUDIO POWER ICs
Figure 5: TDA7375 in S.E. mode with 4 output capacitors
TDA7375
COUT1
+
-
-
+
+
-
-
+
COUT2
COUT3
COUT4
R
CH1+
CH2+ CH3+
CH4+ CH5+
CH5-
CH4-
CH3- CH2-
CH1-
TDA7476
D97AU575A
Figure 6: TDA7375 in S.E. mode with 2 output capacitors
TDA7375
COUT1
+
-
-
+
+
-
-
+
COUT2
R
CH1+
CH2+ CH3+
CH4+ CH5+
CH5-
CH4-
CH3- CH2-
CH1-
TDA7476
D97AU576A
Figure 7: TDA7451
TDA7451
+
-
-
+
+
-
-
+
R
CH1+ CH2+ CH3+ CH4+ CH5+
CH5-
CH4-
CH3- CH2- CH1-
TDA7476
D97AU577A
Figure 8: Quad Bridge Amplifiers
TDA7384, TDA7385, TDA7386, TDA7454
+
-
-
+
+
-
-
+
R
CH1+ CH2+ CH3+ CH4+ CH5+
CH5-
CH4-
CH3- CH2- CH1-
TDA7476
D97AU578A
13/15
TDA7476
mm
DIM.
MIN.
TYP.
inch
MAX.
MIN.
TYP.
MAX.
A
2.35
2.65
0.093
0.104
A1
0.10
0.30
0.004
0.012
A2
2.55
0.100
B
0.33
0.51
0.013
0.0200
C
0.23
0.32
0.009
0.013
D
15.20
15.60
0.598
0.614
E
7.40
7.60
0.291
0.299
e
1.27
0,050
H
10.0
10.65
0.394
0.419
h
0.25
0.75
0.010
0.030
k
OUTLINE AND
MECHANICAL DATA
0° (min.), 8° (max.)
L
0.40
1.27
0.016
SO24
0.050
0.10mm
B
e
A
A2
h x 45°
A1
K
A1
L
.004
H
Seating Plane
D
13
1
12
E
24
SO24
14/15
C
TDA7476
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences
of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is
granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this publication are
subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products
are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.
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15/15