Installation Instructions

LISA-U2 series - System Integration Manual
UBX-13001118 - R19 Early Production Information System description
Page 92 of 175
unidirectional voltage translators (e.g. Texas Instruments SN74AVC4T774 or SN74AVC2T245), using the
module V_INT output as 1.8 V supply for the voltage translators on the module side
For the appropriate selection of a compliant external digital audio device, see +UI2S AT command description in
the u-blox AT Commands Manual [2] for further details regarding the capabilities and the possible settings of I
2
S
digital audio interface of LISA-U2 series modules.
Figure 49 shows an application circuit with a generic digital audio device.
43
I2S_CLK
41
I2S_WA
I
2
S Clock
I
2
S Word Alignment
LISA-U2 series
42
I2S_TXD
44
I2S_RXD
I
2
S Data Input
I
2
S Data Output
GND
GND
1.8 V digital
audio device
Figure 49: I
2
S interface application circuit with a generic digital audio device
As in general any external digital audio device compliant to the configuration of the digital audio interface of the
cellular module can be used with LISA-U2 series modules, 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.
Examples of manufacturers offering compatible audio codec parts, suitable to provide basic analog audio voice
capability on the application device, are the following:
 Maxim Integrated (as the MAX9860, MAX9867, MAX9880A audio codecs)
 Texas Instruments / National Semiconductor
 Cirrus Logic / Wolfson Microelectronics
 Nuvoton Technology
 Asahi Kasei Microdevices
 Realtek Semiconductor
Figure 50 and Table 41 describe an application circuit for I
2
S digital audio interfaces of LISA-U2 series modules,
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.
An I
2
S digital audio interface of the LISA-U2 series modules that acts as an I
2
S master is connected to the digital
audio interface of the external audio codec (that acts as an I
2
S slave). The first I
2
S interface can be used as well as
the second I
2
S interface of the cellular module.
The CODEC_CLK digital output clock of the cellular module is connected to the clock input of the external audio
codec to provide clock reference.
Signal integrity of the high speed lines may be degraded if the PCB layout is not optimal, especially when the
CODEC_CLK clock line or also the I
2
S digital audio interface lines are very long: keep routing short and minimize
parasitic capacitance to preserve signal integrity.
The external audio codec is controlled by the cellular module using the DDC (I
2
C) interface: this interface can be
used to communicate with u-blox GNSS receivers and at the same time to control an external audio codec on all
LISA-U2 series modules.
The V_INT supply output of the cellular module provides the supply to the external audio codec, defining a
proper voltage level for the digital interfaces.