TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R07
Advance Information
Design-in
Page 117 of 158
2.7
Audio interface
2.7.1
Digital audio interface
The I
2
S interface is not available on MPCI-L2 series modules.
2.7.1.1
Guidelines for digital audio circuit design
The I
2
S interface is not supported by TOBY-L2 “00”, “01”, and “50” product versions: the pins should not
be driven by any external device.
I
2
S digital audio interface can be connected to an external digital audio device for voice applications. The external
digital audio device must be properly configured according to the cellular module configuration, with the
opposite role, the same mode, the same sample rate and voltage level.
Any external digital audio device compliant with the configuration of the digital audio interface of the TOBY-L2
cellular module can be used. Examples of compatible audio codec parts, suitable to provide analog audio voice
capability on the application device, are the following:
Marvell 88PM805
Maxim MAX9860
Maxim MAX9867
Maxim MAX9880A
An appropriate specific application circuit has to be implemented and configured according to the particular
external digital audio device or audio codec used and according to the application requirements.
Figure 66 and Table 41 describe an application circuit for the I
2
S digital audio interface providing voice capability
using an external audio voice codec. DAC and ADC integrated in the external audio codec respectively converts
an incoming digital data stream to analog audio output through a mono amplifier and converts the microphone
input signal to the digital bit stream over the digital audio interface.
The module’s I
2
S interface (I
2
S master) is connected to the related pins of the external audio codec (I
2
S slave).
The
GPIO6
of the TOBY-L2 series module (that provides a suitable digital output clock) is connected to the clock
input of the external audio codec to provide clock reference.
The external audio codec is controlled by the wireless module using the DDC (I
2
C) interface: this interface can be
concurrently used to communicate with u-blox GNSS receivers and to control an external audio codec.
The
V_INT
output supplies the external audio codec, defining proper digital interfaces voltage level.
Additional components are provided for EMC and ESD immunity conformity: a 10 nF bypass capacitor and a
series chip ferrite bead noise/EMI suppression filter provided on each microphone line input and speaker line
output of the external codec as described in Figure 66 and Table 41. The necessity of these or other additional
parts for EMC improvement may depend on the specific application board design.
As various external audio codecs other than the one described in Figure 66 / Table 41 can be used to provide
voice capability, the appropriate specific application circuit has to be implemented and configured according to
the particular external digital audio device or audio codec used and according to the application requirements.
