TS4962M_07 Datasheet, PDF (32/41 Pages) STMicroelectronics – 3W filter-free class D audio power amplifier

Application information
TS4962M
We have the following equations:
Out+ – Out-
=
Ve1 ×
--3----0---0---
Rin1
+
…+
Vek
×
--3---0----0---
Rink
(V)
k
Σ ^{Ceq =}
Cinj
j=1
Cinj = _2-----×------_π------_×------R---1--i-n----j---_×------F----C-----L---j
(F)
R_eq = ---------¹----------
k
∑ ^----1-----
j =1 ^Rinj
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 TS4962M inputs.
5.10
Output filter considerations
The TS4962M is designed to operate without an output filter. However, due to very sharp
transients on the TS4962M output, EMI radiated emissions may cause some standard
compliance issues.
These EMI standard compliance issues can appear if the distance between the TS4962M
outputs and loudspeaker terminal is long (typically more than 50mm, or 100mm 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 TS4962M output pins and the
speaker terminals.
● Use ground planes for “shielding” sensitive wires.
● Place, as close as possible to the TS4962M and in series with each output, a ferrite
bead with a rated current at minimum 2A and impedance greater than 50Ω at
frequencies above 30MHz. 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
From TS4962 output
Ferrite chip bead
To speaker
about 100pF
Gnd
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