A21SP16 datasheet(31/37 Pages) STMICROELECTRONICS

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A21SP16

Application information

We have the following equations:

In general, for mixed situations (single-ended and differential inputs), it is best to use the

same rule, that is, to equalize impedance on both A21SP16 inputs.

5.10

Output filter considerations

The A21SP16 is designed to operate without an output filter. However, due to very sharp

transients on the A21SP16 output, EMI radiated emissions may cause some standard

compliance issues.

These EMI standard compliance issues can appear if the distance between the A21SP16

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

directions, to the speaker terminals). As 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 A21SP16 output pins and the

speaker terminals.



Use ground planes for “shielding” sensitive wires.



Place, as close as possible to the A21SP16 and in series with each output, a ferrite

bead with a rated current at minimum 2 A and impedance greater than 50

at

frequencies above 30 MHz. If, after testing, these ferrite beads are not necessary,

replace them by a short-circuit. Murata BLM18EG221SN1 or BLM18EG121SN1 are

possible examples of devices you can use.



Allow enough footprint to place, if necessary, a capacitor to short perturbations to

ground (see the schematics in Figure 63).

Figure 63. Method for shorting pertubations to ground

In the case where the distance between the A21SP16 outputs and speaker terminals is

high, it is possible to have low frequency EMI issues due to the fact that the typical operating

frequency is 250 kHz. In this configuration, we recommend using an output filter (as shown

Out

–

Ve1

300

Rin1

-------------

 Vek

300

Rink

-------------



(V)

Ceq



Cinj

 R

inj F



CLj

----------------------------------------------------

(F)

Req

Rinj

----------



-------------------

Ferrite chip bead

about 100pF

Gnd

From TS4962 output

To speaker

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