CP3SP33SMSSLASHNOPB datasheet(144/407 Pages) TI1

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CP3SP33

SNOSCW5 – MAY 2013

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20.11 Usage Notes

The telematics codec is designed for maximum flexibility, this section gives an overview of recommended

system setups for different applications.

20.11.1 In-Car Bluetooth Telephony

In this mode, the codec acts as a bridge between a Bluetooth-equipped mobile telephone and the car’s

head unit. A GSM phone establishes a link and transmits voice-band audio data in the CVSD format,

which is well-suited to a noisy environment. The data is received by the Bluetooth LLC and passed to the

CVSD decoder. The CVSD converts the data into linear 16-bit samples which are transferred to and from

the codec (possibly through the on-chip DSP). The codec then performs the digital-to-analog and analog-

to-digital conversion and the analog interfaces with the car radio.

Any differences in sample rate should be across the CVSD link where they pose the least threat to audio

quality. The DAC should be used in 8-kHz mode rather than implementing an SRC (Sample Rate

Conversion) scheme. The codec should share a clock source with the Bluetooth LLC.

Data: bidirectional mono 8-kHz 16-bit linear format.

Audio clock for DAC: 2.000 MHz. DACOSR = 00

Audio clock for ADC: 1.000 MHz.

20.11.2 I

2S Music Playback

In this example, the ADC is not used and the data is provided from the I2S interface. The I2S interface

should be configured as a slave to allow the sample rate to be derived from the external source device. If

the source sample rate is not 48 kHz, then SRC is performed in the DSP coprocessor. The sample rate of

the audio stream must be known or conveyed by other means. Data is most likely passed using interrupt

requests. The SRC must cope with the rate conversion and allow for a tolerance in the input rate relative

to the output rate, varying the algorithm to match the required output rate by knowing how often data

arrives and applying skew on the interpolation/decimation when required. This can be avoided by using a

clock synchronous to the audio source and using an oversampling rate other than 125.

Data: Stereo 44.1-kHz 16-bit linear format.

Audio clock for DAC: 12.288 MHz. DACOSR = 01.

20.11.3 Wireless Music Headphones

In this example, the ADC is not used and compressed data is provided from the Bluetooth link. The DSP

must then convert this data into 48-kHz, 16-bit stereo audio for use by the DAC.

Data: Stereo 48-kHz 16-bit linear format.

Audio clock for DAC: 12.000 MHz. DACOSR = 00.

20.11.4 Wireless Voice Headset

In this example, the device is configured in the same way as for In-Car Bluetooth Telephony, but the

output must drive a headphone amplifier rather than the differential line outputs.

20.11.5 MP3 Playback

This application uses the stereo DAC to playback audio from memory, so a PLL can be used to create an

approximate 11.025 MHz clock for 44.1-kHz samples with 12.000 MHz for 48-kHz data.

In this example, the ADC can be used for the typical voice notes feature, 8-kHz recording data in

companded format using the CVSD’s G.711 circuits to compress the data, rather than using a DSP for

compression.

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Telematics Codec

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