TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 111 of 143
2.8.2
Digital audio interface
The second digital audio interface (I2S1) will be supported by future firmware versions.
2.8.2.1
Guidelines for digital audio circuit design
The I
2
S digital audio interfaces can be connected to an external digital audio device for voice applications.
Any external digital audio device compliant with the configuration of the digital audio interface of the TOBY-L4
series cellular module can be used, given that the external digital audio device must provide:
The opposite role: slave or master role, as TOBY-L4 series modules may act as master or slave
The same mode and frame format: PCM / short synch mode or Normal I
2
S / long synch mode with
o
data in 2’s complement notation, linear
o
MSB transmitted first
o
data word length = 16-bit (16 clock cycles)
o
frame length = synch signal period:
17-bit or 18-bit in PCM / short alignment mode (16 + 1 or 16 + 2 clock cycles, with the Word
Alignment / Synchronization signal set high for 1 clock cycle or 2 clock cycles)
32-bit in Normal I
2
S mode / long alignment mode (16 x 2 clock cycles)
The same sample rate, i.e. synch signal frequency, <I2S_sample_rate> parameter:
o
8 kHz, 11.025 kHz, 12 kHz, 16 kHz, 22.05 kHz, 24 kHz, 32 kHz, 44.1 kHz, 48 kHz, 96 kHz, 192 kHz
The same serial clock frequency:
o
17 x <I2S_sample_rate> or 18 x <I2S_sample_rate> in PCM / short alignment mode, or
o
16 x 2 x <I2S_sample_rate> in Normal I
2
S mode / long alignment mode
Compatible voltage levels (1.80 V typ.), otherwise it is recommended to connect the 1.8 V digital audio
interface of the module to the external 3.0 V (or similar) digital audio device by means of appropriate
unidirectional voltage translators (e.g. TI SN74AVC4T774 or SN74AVC2T245, providing a partial power
down feature so that the digital audio device 3.0 V supply can be also ramped up before
V_INT
1.8 V
supply), using the module
V_INT
output as 1.8 V supply for the voltage translators on the module side.
An appropriate specific application circuit must 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 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 66 and Table 50 describe application circuits for the digital audio interfaces, considering these scenarios:
1.8 V digital audio device with slave role connected to a digital audio interface of the module set as master
1.8 V digital audio device with master role connected to a digital audio interface of the module set as slave
3.0 V digital audio device with slave role connected to a digital audio interface of the module set as master
3.0 V digital audio device with master role connected to a digital audio interface of the module set as slave
The same circuits can be implemented for both the I2S0 and the I2S1 digital audio interfaces of the module.