TS4999

Application information

29/36

4.9

Output filter considerations

The TS4999 is designed to operate without an output filter. However, due to very sharp

transients on the TS4999 output, EMI-radiated emissions may cause some standard

compliance issues.

These EMI standard compliance issues can appear if the distance between the TS4999

outputs and loudspeaker terminal are long (typically more than 50 mm, or 100 mm in both

directions, to the speaker terminals). Because the PCB layout and internal equipment

device are different for each configuration, it is difficult to provide a one-size-fits-all solution.

However, to decrease the probability of EMI issues, there are several simple rules to follow.

●

Reduce, as much as possible, the distance between the TS4999 output pins and the

speaker terminals.

●

Use a ground plane for "shielding" sensitive wires.

●

Place, as close as possible to the TS4999 and in series with each output, a ferrite bead

with a rated current of at least 2.5 A and impedance greater than 50-

Ω at frequencies

above 30 MHz. If, after testing, these ferrite beads are not necessary, replace them by

a short-circuit.

●

Allow extra footprint to place, if necessary, a capacitor to short perturbations to ground

(see Figure 60).

Figure 60.

Ferrite chip bead placement

In the case where the distance between the TS4999 output and the speaker terminals is too

long, it is possible to encounter low frequency EMI issues due to the fact that the typical

operating PWM frequency is 280 kHz and that the fall and rise time of the output signal is

less than or equal to 5 ns. In this configuration, it is necessary to use the output filter

represented in Figure 61 on page 30, which consists of L1, C1, L2 and C2 being placed as

close as possible to the TS4999 outputs.

In particular cases where the output filter is used and there is the possibility to disconnect a

load, we recommended using an RC network that consists of C3 and R, as shown in

Figure 61. In this case, when the output filter is connected without any load, the filter acts as

a short-circuit for frequencies above 10 kHz in the output frequency spectrum of the

amplifier. The RC network corrects the frequency response of the output filter and

compensates this limitation.

to speaker

about 100pF

gnd

Ferrite chip bead

From output