FDA803D datasheet(46/78 Pages) STMICROELECTRONICS

46 / 78 page

Diagnostic

FDA803D

46/78

DocID031487 Rev 2

Figure 57. Hot spot detection

In standard operative condition, the DC value of IOUTP and IOUTM is zero, therefore the

measured output current offset is zero.

When a soft short is connected between one output and Vcc or Gnd, the corresponding

output drives an additional current ISHORT. The device interprets half of the mentioned

current as offset: IOFFSET = |IOUTP-IOUTM|/2 = |ISHORT|/2.

In conclusion, if half of the DC current flowing in the short circuit exceeds the threshold

selected through IB10[4,3], Output Current Offset Detector communicates an offset

detection.

11.8

PWM pulse skipping detector

Pulse skipping detector aim is to detect the PWM stage saturation.

The feature detects pulse skipping when, for each output, at least two consecutive PWM

commutations have been skipped. The operation is shown in Figure 58:

Figure 58. PWM pulse skipping detector operation

In order to enable the PWM pulse skipping detector, the user must set IB5[5,4]='01'.

When detecting pulse skipping, the feature provides the output in two forms:



Enables the pull down on CDDiag pin



Sets the flag DB1[0]='1'

As soon as the pulse skipping condition is removed, both the outputs are reset.

The suggested utilization for this function is to connect a low-pass filter to CDDiag pin,

therefore comparing the output with a voltage threshold. The lower is the CDDiag pin

average voltage, the higher is the distortion.

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