TDA7476 Fast Delivery |IC PHOENIX CO.,LIMITED

TDA7476 ,CAR RADIO DIAGNOSTIC PROCESSORELECTRICAL CHARACTERISTICS (continued)(V = 14.4V; T = 25°, unless otherwise specified.)s ambSymbol ..
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TDA7476
CAR RADIO DIAGNOSTIC PROCESSOR
1/19
TDA7476
April 2001 WIDE OPERATING VOLTAGE RANGE ST-BY FUNCTION (C-MOS) LOW QUIESCENT ST-BY CURRENT
CONSUMPTIONI2 C 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 PROTECTORS 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 appli-
cations. It is able to detect potential faults coming
from any misconnection in the car radio or in the har-
ness 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 com-
patible) in order to disable the ICs under fault and/or
to alert the micro-controller by means of warning
messages.
CAR RADIO DIAGNOSTIC PROCESSOR
PIN CONNECTION (Top view)
TDA7476
2/19
BLOCK DIAGRAM & APPLICATION CIRCUIT
PIN FUNCTION
3/19
TDA7476
ABSOLUTE MAXIMUM RATINGS
(*) Minimum value between VS+10V and 25V.
THERMAL DATA
ELECTRICAL CHARACTERISTICS
(Vs = 14.4V; Tamb = 25°, unless otherwise specified.)
TDA7476
4/19
ELECTRICAL CHARACTERISTICS (continued)
(Vs = 14.4V; Tamb = 25°, unless otherwise specified.)
5/19
TDA7476
ELECTRICAL CHARACTERISTICS (continued)
(Vs = 14.4V; Tamb = 25°, unless otherwise specified.)
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 is
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.
TDA7476
6/19 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) · 11
Isource = 1.5 · Isink 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 (S.C.), normal
operation and open load are detected as following:
where Lsc, Lnop, Lop as specified in the ELCTRICAL CHARACTERISTICS.
For example, here below are two cases, with Rcs = 3.3KOhm and Rcs = 1.8KOhm..
The exact values of the above mentioned resistive ranges may vary a little, depending on the power amplifier
used.
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 volt-
age 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: L sc,max ksin
------------------- L sc,max
36.3--------- ---------- Rcs⋅== L nop,min ksin
---------------------- L nop,min
36.3------ ----------------Rcs⋅== L nop,max ksin
----------------------- L nop,max
36.3------------ ----------- Rcs⋅== L op,max ksin
-------------------- Lop min,
36.3------ -------------- Rcs⋅==
7/19
TDA7476
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.
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 volt-
age 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 admis-
sible. The detection ranges can be set by adjusting the sensing resistors Rsens1 or Rsens2 as following:
Where AOL, Anop, Agnd are as specified in the ELECTRICAL CHARACTERISTICS.
For example, if Rsens = 5 Ohm, the following detection table will be operative :
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-0.6V 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.3 nop,min sens
----------- -----------=2 nop,max sens
------ ------------------=1 gnd,min sens
--- -------------------=
TDA7476
8/19
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 mP must wait a period Twait1(see Software Specification)
that is depending on the timing capacitor CT according to the following table (Twait1> tm, max):
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 · 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 · CT/10μF)ms
For bridge or bridge equivalent devices (figg.5,6), Ct = 10μF will be enough.
TURN-ON DIAGNOSTIC - THRESHOLDS
CH1, CH2, CH3, CH4, CH5 Output voltage during test. (The power amplifier must be in ST-BY mode). Voltage across the load during test. (The power amplifier must be in ST-BY mode). 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.
9/19
TDA7476
The following table shows the result pointed out by TDA7476 when multiple misconnections are present:
(*) CH means CH+ or CH-
AUX1 - AUX2 Voltage across the sensing resistors 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
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".
TDA7476
10/19 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).2 C BUS INTERFACE
Data transmission from microprocessor to the TDA7476 and viceversa takes place through the 2 wires I2 C 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.
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 pull-down (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
Figure 2. Data Validity on the I2 CBUS

Partno	Mfg	Dc	Qty	Available	Descript
TDA7476	ST	N/a	912	avai	CAR RADIO DIAGNOSTIC PROCESSOR