FDA803D datasheet(43/78 Pages) STMICROELECTRONICS

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FDA803D

Diagnostic

Please note that an exact value of impedance can be defined only in case of an ideal

sinusoid at a fixed frequency. In case of a generic audio signal, the overall complex

impedance vs frequency characteristic of the speaker is involved.

11.4.5

I2C control and timing

The user must set IB3[0] in order to start the open load in play detection.

Once the test is started, the internal circuits required for the detection are turned on,

requiring a settling time lasting approximately 500 ms.

When the internal circuits are ready to work, both digital input signal and output current

measurement start being evaluated, following the impedance threshold set through IB10[6].

Depending on the audio signal characteristics, the evaluation can last from 300 ms to 1 s

approximately.

At the end of the evaluation, the device:



Sets DB0[2]='1' to communicate that the test ended successfully, and resets IB3[0]

allowing the user to perform another test afterwards



Sets DB0[1]='1' to communicate that the test result is valid, otherwise sets DB0[1]='0' to

communicate that the test result is not valid.



Sets DB0[0]='1' to communicate that an open load has been detected, otherwise sets

DB0[0]='0' to communicate that an open load has not been detected.

Please note that the value on DB0[0] is significant only if the test result is valid.

If the test ends successfully but the result is not valid, the user must repeat the test. This

condition happens when the audio signal is not good enough for a reliable detection.

The detection timings are represented in Figure 54:

Figure 54. Open load in play detector timing

If the device FSM moves from PLAY to another state during the open load in play detection

routine, the test ends unsuccessfully by keeping the flag DB0[2] clear. The device

automatically resets IB3[0] allowing the user to repeat the test.

11.5

Input offset detector

Input offset detector aim is to detect an offset coming from the audio signal source through

I2S/TDM input stream.

For this purpose, the feature evaluates the input offset through a low-pass filter, which is

compared with a threshold equal to -18dBFs. If the measured offset exceeds the threshold,

Input Offset Detector sets the flag DB0[7] to '1'.

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