FDA903U datasheet(40/80 Pages) STMICROELECTRONICS

40 / 80 page

Diagnostic

FDA903U

40/80

DS12498 Rev 2

10.4

Open load in play detector

The open load in play detector aim is to detect the possible speaker detachment during

PLAY state.

The innovative internal architecture allows to detect an open load condition taking

advantage of the audio signal itself, guaranteeing high detection reliability without requiring

a dedicated test signal.

10.4.1

Open load in play detector operation overview

The open load in play detection consists in one single shot test, which can be repeated

according to the user's need.

The test firstly checks the audio signal characteristics. If the audio signal is judged good

enough to provide a reliable result, the test result is valid. Otherwise, if the audio signal

doesn't allow to perform a reliable detection, the test result is not valid and the user needs to

repeat the test.

During the same evaluation time window, an internal circuit measures the differential current

flowing through the pins OUTP and OUTM. The test consequently evaluates both the digital

input signal and the output current, monitoring the average load impedance over time.

If the test result is valid and the average load impedance exceeds the chosen impedance

threshold, the device communicates that the load is not connected. Otherwise, if the test

result is valid and the average load impedance is lower than the chosen threshold, the

device communicates that the load is connected.

10.4.2

Processing bandwidth range

The feature requires an accurate measurement of the current flowing through the speaker.

The filter capacitors behave like an undesired load connected in parallel with the speaker,

altering the current measurement. However, this undesired contribution is significant only in

the high frequency range of the audio bandwidth.

On the other side, most of the audio signal energy is distributed in the midde-low frequency

range of the audio bandwidth.

Due to the mentioned reasons, Open Load in Play Detector processes the audio bandwidth

up to 2kHz approximately, in order to guarantee a highly reliable solution without affecting

the rate of valid tests.

Please note that the processing bandwidth limitation does not affect the main signal path

from digital input signal to output voltage on FBP and FBM pins.

FDA903U датащи(PDF) 40 Page - STMicroelectronics