Cirrus Logic CS5378 - Manual (Page 62)

CS5378
DS639F3 62
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
ΔΣ 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
ΔΣ 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.