LC filter transient/over voltage suppression

"mj"

Sec 3.1.1 of the datasheet

says "The TDA2003A has a circuit which enables it to withstand a voltage pulse train, on pin 5, of the type shown in Figure 23. If the supply voltage peaks to more than 40 V, then an LC filter must be inserted between the supply and pin 5, in order to ensure that the pulses at pin 5 will be held within the limits shown in Figure 22. A recommended LC network is shown in Figure 23. With this network, a train of pulses with amplitude up to 120 V and width of 2 ms can be applied at point A. This type of protection is ON when the supply voltage (pulsed or DC) exceeds 18 V. For this reason the maximum operating supply voltage is 18 V."

Figure 23 is LC Filter is 2mH series inductor at input and 3300uf parallal capacitor to GND. Absolute maximum supply voltage to the IC is 40V. How can LC filter protect the amplifier from up to 120V pulses as claimed? Is it like attenuating the signal above the cutoff frequency ?

What I understand from this sec of datasheet is the lc filter comes into effect between 18V and 120V input pulses. If I am not wrong, the LC filter discussed can low pass and attenuate the transients above its cutoff irrespective of peak voltage. Why is voltage coming into the picture?

** The transient pulses all have the same polarity, so there is a significant DC component.

Presumably, the rise in voltage on the 3300uF cap is still reasonably small when 120V pulses are applied, 2mS long and repeated not more than once per second.

.... Phil

The capacitor is rated 16V in the datasheet. Even if the lc filter clamps to 40V can the capacitor withstand?

mj

"mj"

** The LC filter is not a voltage clamp, it simply attenuates voltage spikes.

... Phil