NXP Semiconductors
UM10340_5
TFA9879 demonstration PCB
© NXP B.V. 2011. All rights reserved.
User manual
Rev. 05 — 30 aug. 2011
7 of 20
L
E
R
DC
2.1.3 Speaker dummy load
The TFA9879 is a filter-free Class-D amplifier that will directly drive the loudspeaker. For
realistic measurement at a filter-free Class-D amplifier a dummy load, consisting out of a
resistor (R
DC
) in series with an inductor (L
E
), should replace the loudspeaker. The resistor
represents the loudspeaker dc resistance and the inductor (L
E
) represents the
loudspeaker coil.
Figure 4: Simplified loudspeaker model
Measurement at the demonstration PCB are performed with resistor of R
DC
= 8
Ω
, L
E
=
44
µ
H or R
DC
= 4
Ω
, L
E
= 20
µ
H. But inductor values between respectively 15
µ
H and 60
µ
H
are suitable (saturation current >1.5A) for measurements as well.
