TDA7575 Datasheet TDA7575 | P13-P15

13/17

TDA7575

The information related to the outputs status is read and memorized at the end of the current pulse top. The

acquisition time is 100 ms (typ.). No audible noise is generated in the process. As for SHORT TO GND / Vs the

fault-detection thresholds remain unchanged from 26 dB to 12 dB gain setting. They are as follows:

Concerning SHORT ACROSS THE SPEAKER / OPEN SPEAKER, the threshold varies from 26 dB to 12 dB

gain setting, since different loads are expected (either normal speaker's impedance or high impedance). The

values in case of 26 dB gain are as follows:

If the Line-Driver mode (Gv= 12 dB and Line Driver Mode diagnostic = 1) is selected, the same thresholds will

change as follows:

b) PERMANENT DIAGNOSTICS

Detectable conventional faults are:

–SHORT TO GND

–SHORT TO Vs

– SHORT ACROSS THE SPEAKER

The following additional features are provided:

– OUTPUT OFFSET DETECTION

The TDA7575 has 2 operating statuses:

1) RESTART mode. The diagnostic is not enabled. Each audio channel operates independently from each oth-

er. If any of the a.m. faults occurs, only the channel(s) interested is shut down. A check of the output status is

made every 1 ms (fig. G). Restart takes place when the overload is removed.

2) DIAGNOSTIC mode. It is enabled via I

C bus and self activates if an output overload (such to cause the in-

tervention of the short-circuit protection) occurs to the speakers outputs . Once activated, the diagnostics pro-

cedure develops as follows (fig. H):

– To avoid momentary re-circulation spikes from giving erroneous diagnostics, a check of the output

status is made after 1ms: if normal situation (no overloads) is detected, the diagnostic is not per-

formed and the channel returns back active.

– Instead, if an overload is detected during the check after 1 ms, then a diagnostic cycle having a du-

ration of about 100 ms is started.

– After a diagnostic cycle, the audio channel interested by the fault is switched to RESTART mode. The

D02AU1341

S.C. to GND x S.C. to Vs

0V 1.8V V

-1.5V V

xNormal Operation

1.2V V

-0.9V

S.C. across Load x Open Load

0V 1.5Ω 70Ω Infinite

xNormal Operation

0.5Ω

130Ω

D01AU1254

D01AU1252

S.C. across Load x Open Load

0Ω 4.5Ω 200Ω infinite

xNormal Operation

1.5Ω 400Ω

TDA7575

14/17

relevant data are stored inside the device and can be read by the microprocessor. When one cycle

has terminated, the next one is activated by an I

C reading. This is to ensure continuous diagnostics

throughout the car-radio operating time.

– To check the status of the device a sampling system is needed. The timing is chosen at microproces-

sor level (over than half a second is recommended).

Fig. G: Restart timing without Diagnostic Enable (Permanent)

Each 1mS time, a sampling of the fault is done

Fig H: Restart timing with Diagnostic Enable (Permanent)

OUTPUT DC OFFSET DETECTION.

Any DC output offset exceeding +/- 2 V are signalled out. This inconvenient might occur as a consequence of

initially defective or aged and worn-out input capacitors feeding a DC component to the inputs, so putting the

speakers at risk of overheating.

This diagnostic has to be performed with low-level output AC signal (or Vin = 0).

The test is run with selectable time duration by microprocessor (from a "start" to a "stop" command):

– START = Last reading operation or setting IB1 - D5 - (OFFSET enable) to 1

– STOP = Actual reading operation

Excess offset is signalled out if persistent throughout the assigned testing time. This feature is disabled if any

overloads leading to activation of the short-circuit protection occurs in the process.

circuit protection intervention

1-2mS

1mS 1mS 1mS

1mS

Overcurrent and short

(i.e. short circuit to GND)

Short circuit removed

Out

circuit protection intervention

Overcurrent and short

(i.e. short circuit to GND)

Short circuit removed

1mS 100mS 1mS1mS

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TDA7575

MULTIPLE FAULTS.

When more misconnections are simultaneously in place at the audio outputs, it is guaranteed that at least one

of them is initially read out. The others are notified after successive cycles of I

C reading and faults removal,

provided that the diagnostic is enabled. This is true for both kinds of diagnostic (Turn on and Permanent).

The table below shows all the couples of double-fault possible. It should be taken into account that a short circuit

with the 4 ohm speaker unconnected is considered as double fault.

Double fault table for Turn On Diagnostic

S. GND (so) / S. GND (sk) in the above table make a distinction according to which of the 2 outputs is shorted

to ground (test-current source side= so, test-current sink side = sk). More precisely, in both the Channels SO =

CH+, and SK = CH-.

In Permanent Diagnostic the table is the same, with only a difference concerning Open Load(*) , which is not

among the recognisable faults. Should an Open Load be present during the device's normal working, it would

be detected at a subsequent Turn on Diagnostic cycle (i.e. at the successive Car Radio Turn on).

FAULTS AVAILABILITY

All the results coming from I

Cbus, by read operations, are the consequence of measurements inside a defined

period of time. If the fault is stable throughout the whole period, it will be sent out. This is true for DC diagnostic

(Turn on and Permanent), for Offset Detector.

To guarantee always resident functions, every kind of diagnostic cycles (Turn on, Permanent, Offset) will be

reactivate after any I2C reading operation. So, when the micro reads the I

C, a new cycle will be able to start,

but the read data will come from the previous diag. cycle (i.e. The device is in Turn On state, with a short to Gnd,

then the short is removed and micro reads I2C. The short to Gnd is still present in bytes, because it is the result

of the previous cycle. If another I2C reading operation occurs, the bytes do not show the short). In general to

observe a change in Diagnostic bytes, two I2C reading operations are necessary.

C PROGRAMMING/READING SEQUENCES

A correct turn on/off sequence respectful of the diagnostic timings and producing no audible noises could be as

follows (after battery connection):

– TURN-ON: (STAND-BY OUT + DIAG ENABLE) --- 500 ms (min) --- MUTING OUT

– TURN-OFF: MUTING IN --- 20 ms --- (DIAG DISABLE + STAND-BY IN)

Car Radio Installation: DIAG ENABLE (write) --- 200 ms --- I

C read (repeat until All faults disappear).

– OFFSET TEST: Device in Play (no signal) --

– OFFSET ENABLE - 30ms - I

C reading

(repeat I

C reading until high-offset message disappears).

S. GND (sc) S. GND (sk) S. Vs S. Across L. Open L.

S. GND (sc) S. GND S. GND S. Vs + S. GND S. GND S. GND

S. GND (sk) / S. GND S. Vs S. GND Open L. (*)

S. Vs / / S. Vs S. Vs S. Vs

S. Across L. / / / S. Across L. N.A.

Open L. / / / / Open L. (*)

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P17

TDA7575

Mfr. #:

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STMicroelectronics

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IC AMP AUDIO 150W AB 27FLEXIWATT

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