Sierra Wireless WISMO218 - Manual (Page 56)

WA_DEV_W218_PTS_002 Rev 005 Page 56 of 109
Product Technical Specification &
Customer Design Guidelines
Speaker SPKP and SPKN
SPK Differential Connection
SPKP
SPKN
Figure 19. Example of Speaker Differential Connection
SPK Single-Ended Connection
Typical implementation:
SPKP
C1
+
SPKN
Z hp Speaker
C3 33 pF
to
100 pF
X
Figure 20. Example of Speaker Single-Ended Connection
4.7µF < C1 < 47 µF (Depending on speaker characteristics and output power.)
Using a single-ended connection includes losing output power (-6dB) as compared to a differential
connection.
The connection between the WISMO218 pins and the speaker must be designed to keep the serial
impedance lower than 1.5 in a single-ended connection.
SPKN can be left open in a single-ended connection.
Design Recommendation
General
When both speaker and microphone are exposed to the external environment, it is recommended to
add ESD protection as close as possible to the speaker or microphone, connected between the audio
lines and a good ground.
When using the single-ended connection of MICP, ensure to have a good ground plane, good filtering
as well as shielding, in order to avoid any disturbance on the audio path.