TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 109 of 143
Guidelines for connecting one external analog audio device input
Figure 65 and Table 49 describe application circuits connecting the downlink path of the analog audio interface
of TOBY-L4 series modules to analog audio input of generic external analog audio devices:
One differential analog audio input is connected to an analog audio downlink path of the module
One single-ended analog audio input is connected to an analog audio downlink path of the module
Guidelines for the connection to a differential analog audio input:
The
SPK_P
/
SPK_N
balanced output of the module must be connected to the differential input of the
external audio device by means of series capacitors for DC blocking (e.g. 10 µF) to decouple the bias present
at the module output, as illustrated in the left side of Figure 65.
Guidelines for the connection to a single-ended analog audio input:
A suitable differential to single-ended circuit must be inserted from the
SPK_P
/
SPK_N
balanced output of
the module to the single-ended input of the external audio device, as illustrated in the Figure 65 right side:
10 µF series capacitors are provided to decouple the bias present at the module output, and a voltage
divider is provided to properly adapt the signal level from module output to external audio device input.
Additional guidelines for any connection:
Audio devices with differential analog I/O are preferable, as they are more immune to external disturbances.
The DC-block series capacitor acts as a high-pass filter for audio signals, with a cut-off frequency depending
on both the values of capacitor and on the input impedance of the device. For example: for differential input
impedance of 600
, the two 10 µF capacitors will set the -3 dB cut-off frequency to 53 Hz, while for
single-ended connection to a 600
external device, the cut-off frequency with just the single 10 µF
capacitor will be 103 Hz. In both cases. the high-pass filter has a low enough cut-off for the correct
frequency response.
Use a suitable power-on sequence to avoid audio bump due to charging of the capacitor: the final audio
stage should be always enabled as the last one.
The signal levels can be adapted by setting the internal gains, but additional circuitry must be inserted if
SPK_P
/
SPK_N
output level of the module is too high for the audio device input, as the voltage dividers
present in the circuits illustrated in Figure 65 right side to properly adapt the signal level.
TOBY-L4 series
C1
C2
SPK_N
SPK_P
GND
Analog IN (-)
Analog IN (+)
Audio Device
GND
TOBY-L4 series
SPK_N
SPK_P
GND
Analog IN
Audio Device
GND
C3
C4
R2
R1
Figure 65: Application circuits to connect the module to audio devices with suitable differential or single-ended input
Reference
Description
Part Number – Manufacturer
C1, C2, C3, C4
10 µF Capacitor X5R 0603 5% 6.3 V
GRM188R60J106M – Murata
R1
0
Ω
Resistor 0402 5% 0.1 W
RC0402JR-070RL – Yageo Phycomp
R2
Not populated
Table 49: Example of components for connecting audio devices with suitable analog differential or single-ended input
