TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 108 of 143
Guidelines for connecting an external high-power loudspeaker
Figure 64 and Table 48 show an application circuit connecting the downlink path of the analog audio interface
of TOBY-L4 series modules to a high-power loudspeaker:
An external 8
or 4
loudspeaker is connected to the analog audio downlink path of the module through
an external audio amplifier, which must be provided on the application board to amplify the low power
audio signal provided by the downlink path of the module.
As in the example circuit in Figure 64 and Table 48, the following general guidelines are recommended for the
design of an analog audio circuit connecting a high-power loudspeaker:
Provide a DC blocking series capacitor at both
SPK_P
and
SPK_N
analog downlink outputs (C1 and C2
Murata GRM155R71C473K 47 nF capacitors in Figure 64). Then connect the lines to the differential input of
a suitable external audio amplifier, the differential output of which must be connected to the 8
or 4
loudspeaker. (See the Analog Devices SSM2305CPZ filter-less mono 2.8 W class-D Audio Amplifier in the
circuit illustrated in Figure 64.)
Provide suitable parts on each line connected to the external loudspeaker as noise and EMI improvements, to
minimize RF coupling, according to the EMC requirements of the custom application.
o
Mount a 27 pF bypass capacitor (e.g. Murata GRM1555C1H270J) from each loudspeaker line to the
solid ground plane (C3 and C4 capacitors in Figure 64).
Provide additional ESD protection (e.g. Bourns CG0402MLE-18G varistor) if the analog audio lines will be
externally accessible on the application device, according to the EMC/ESD requirements of the custom
application. The protection should be mounted close to an accessible point of the line (D1 and D2 parts in
the circuit illustrated in Figure 64).
TOBY-L4 series
SPK_P
SPK_N
C3
C4
LSPK
Loud-Speaker
Connector
J1
OUT+
IN+
GND
U1
OUT-
IN-
C1
C2
R1
R2
VDD
C6
C5
Audio
Amplifier
VCC
D1
D2
Figure 64: Application circuit connecting the analog audio interface to a high-power loudspeaker
Reference
Description
Part Number – Manufacturer
C1, C2
47 nF Capacitor Ceramic X7R 0402 10% 16V
GRM155R71C473KA01 – Murata
C3, C4
27 pF Capacitor Ceramic C0G 0402 5% 25 V
GRM1555C1H270JA01 – Murata
C5
10 µF Capacitor Ceramic X5R 0603 20% 6.3 V
GRM188R60J106ME47 – Murata
C6
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R71C104KA88 – Murata
D1, D2
Low Capacitance ESD Protection
CG0402MLE-18G - Bourns
J1
Speaker Connector
Various Manufacturers
LSPK
8
Loud-Speaker
Various Manufacturers
MIC
2.2 k
Electret Microphone
Various Manufacturers
R1, R2
0
Resistor 0402 5% 0.1 W
RC0402JR-070RL – Yageo Phycomp
U1
Filter-less Mono 2.8 W Class-D Audio Amplifier
SSM2305CPZ – Analog Devices
Table 48: Example of components for connecting the analog audio interface to a high-power loudspeaker
