TDA7801SM datasheet(25/48 Pages) STMICROELECTRONICS

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TDA7801

Functional description

Figure 29. Short to GND and short to Vs, threshold description

Concerning short across the speaker / open speaker, the threshold varies from speaker

mode to booster mode diagnostic setting, since different loads are expected (either normal

speaker's impedance or high impedance). The speaker or booster mode is selected with bit

D6-IB0 (channel 1 and 3) and bit D5-IB0 (channel 2 and 4). The values in case of speaker

mode gain are as in Figure 30.

Figure 30. Short across the speaker and open load threshold description, in amplifier

mode.

If the booster mode is selected, the same thresholds will change as in Figure 31.

Figure 31. Short across the speaker and open load threshold description, in line

driver mode.

When the amplifier is biased and the diagnostic is still enabled the permanent diagnostic

takes place. The previous turn-on state is kept until a short appears at the outputs because

only in this case a new diagnostic cycle can start.

6.3

Permanent diagnostic

Detectable conventional faults are:



Short to GND



Short to Vs



Short across the speaker

The following additional features are provided:



Output offset detection



AC diagnostic

The TDA7801 diagnostic has 2 different cycles:

Restart cycle. It is a 1 ms pulse. During this period a check of the outputs is made.

Plateau cycle. It is a 100 ms pulse. During this period a check of the outputs is

performed and the result of diagnostic analysis is communicated by means of I2C bus.

The TDA7801 has 2 different operating behaviors when a fault occurs:

Restart mode, (D6-IB0='0'). The diagnostic is not enabled. Each audio channel

operates independently of each other. If any of the a.m. faults occurs, only the

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