CS5378 datasheet(62/88 Pages) CIRRUS

62 / 88 page

CS5378

DS639F2

17.6 TBS Loopback Testing

Included as part of the CS5378 test bit stream gen-

erator is a feedback path to the digital filter MDA-

TA input. This loopback mode provides a fully

digital signal path to test the TBS generator, digital

filter, and data collection interface. Digital loop-

back testing expects 512 kHz

∆Σ data into the

MDATA input.

A mismatch of the TBS generator full scale output

and the MDATA full scale input results in an am-

plitude mismatch when testing in loopback mode.

The TBS generator outputs a 75% maximum one’s

density, while the MDATA inputs expect an 86%

maximum one’s density from a

∆Σ modulator, re-

sulting in a measured full scale error of approxi-

mately -3.6 dB.

17.7 TBS Synchronization

When the TSYNC bit is set in the TBSCFG regis-

ter, the MSYNC signal resets the sine wave data

pointer and phase aligns the TBS signal output.

Once the digital filter is settled, all CS5378 devices

receiving the SYNC signal will have identical TBS

signal phase. See “Synchronization” on page 24

for more information about the SYNC and

MSYNC signals.

If TSYNC is clear, MSYNC has no effect on the

TBS data pointer and no change in the TBS output

phase will occur during synchronization.

CS5378 Datasheet(PDF) 62 Page - Cirrus Logic