CP2114 datasheet(21/44 Pages) SILABS

21 / 44 page

CP2114

Rev. 1.1

5.6. CP2114 Clock Configuration

The CP2114 always reports its capabilities to the USB host at a sample rate of 48 kHz and sample size of 16 bits.

For source audio files differing from this format the USB host will automatically perform sample rate conversion.

The CP2114 has the following configuration options:

Table 19 shows all possible clock configuration settings for the CP2114. The CP2114 divides the USB source clock

by 4 so a clock of 48 MHz provides the 12 MHz clock needed for USB. The CP2114 divides the system clock by 4

to derive MCLK. So a 48 MHz system clock will generate MCLK = 12 MHz. If the CP2114 is configured to operate

in Asynchronous mode, it will automatically use explicit feedback to the host. If it is configured for Synchronous

mode, then the sample synchronization method is noted in the table. There are a number of invalid clocking

configurations that result from either the USB clock not resulting in 12 MHz or the MCLK/LRCK not being an

integer divisor. Operating in asynchronous mode is recommended because it best accommodates any mismatch in

host/CP2114 clocks. Operating in synchronous mode requires the CP2114 to adjust its internal oscillator to match

the host sample rate, or to periodically drop or repeat an audio sample if SYSCLK is driven by an External Clock.

Table 18. Clock Configuration Options

Configuration Parameter

Options

Stream Type

Asynchronous

Synchronous

USB Clock Source

Internal

External

System Clock Source

Internal

External

System Clock Frequency

48 MHz

49.152 MHz

MCLK/LRCK Ratio

250

256

Table 19. Valid Clock Configuration Modes

Mode

USB

Clock

(USBCLK)

Source

System

Clock

(SYSCLK)

Source

Int Freq

(MHz)

MCLK/

LRCK

Ratio

Ext Osc

Freq

(MHz)

Notes

1Int

Int

250

 Lowest cost - no external clock required

 Audio device must support 12.0 MHz MCLK

 Sync mode: IntOsc adjusted to

accommodate clock mismatch

Int

Ext

256

49.152

 Async mode: best audio quality

 Sync mode: must drop/repeat samples to

accommodate clock mismatch

3Ext

Int

49.152

250

256

 IntOsc frequency dictated by audio device

MCLK/LRCK ratio

 Sync mode: IntOsc adjusted to

accommodate clock mismatch

4Ext

Ext

250

 Audio device must support 12.0 MHz MCLK

 Async mode: best audio quality

 Sync mode: must drop/repeat samples to

accommodate clock mismatch

CP2114 Datasheet(PDF) 21 Page - Silicon Laboratories

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