FDA903D datasheet(42/82 Pages) STMICROELECTRONICS

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Diagnostic

FDA903D

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DocID031502 Rev 2

11.4.3

Audio signal evaluation

The audio signal is considered a good test signal if its amplitude allows the internal circuits

to perform accurate measurements. In particular, Open Load in Play Detector processes the

audio signal only if its amplitude exceeds the values expressed in Table 9:

The audio signal is unknown and not stationary, while the speaker has a complex

impedance. Open Load in Play Detector evaluates the audio signal for a time window lasting

up to 1s in order to properly average the data over time. The detection is considered valid if,

during the evaluation time window, the input audio signal exceeds for 300ms the thresholds

reported in Table 9.

11.4.4

Impedance threshold

Open Load in Play Detector includes two different impedance thresholds which can be

configured through IB10[6] and which depend also on gain setting through IB6[4]. Their

value has been calibrated in the following conditions:



ideal sinusoidal signal,



absence of external disturbances.

The uncertainly on audio signal characteristics and on external disturbances requires to

keep proper tolerances. The guaranteed thresholds are reported in Figure 52 and in

Figure 53:

Figure 52. Open load in play detector guaranteed thresholds with standard gain

setting

Figure 53. Open load in play detector guaranteed thresholds with low gain setting

Table 9. Open load in play detector impedance and validity thresholds

Open load impedance threshold

Digital input signal amplitude threshold

25 Ω (IB10[6]=’0’)

67 mFs

15 Ω (IB10[6]=’1’)

40 mFs

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