cs5378 Cirrus Logic, Inc., cs5378 Datasheet - Page 62

• Manufacturer Part Number: cs5378
• Description: Low-power Single-channel Decimation Filter
• Manufacturer: Cirrus Logic, Inc.

17.6 TBS Impulse Output
If the TMODE bit in TBSCFG is set high, the TBS
generator operates in impulse mode. In this mode,
the value in TBSGAIN sets the amplitude of the
generated impulse. Impulse amplitude and period
are shown in Table 19.
To create a maximum impulse from the TBS gen-
erator, the TBSGAIN register should be set to
0x04FFFF, and the INTP bits in TBSCFG should
also be set to 0xFF. The RATE bits should always
be set to produce data at the correct rate for the in-
tended test DAC.
A rising edge on the TIMEB pin triggers the im-
pulse output. When impulse mode is enabled but
no TIMEB input is received, the TBS generator
uses a negated TBSGAIN register as a repetitive in-
put value. When a rising edge is recognized on the
TIMEB pin, a single positive TBSGAIN value is
written to the TBS generator to create the impulse.
17.7 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
DS639F1
Test Bit Stream Impulse Characteristics:
Interpolation
Selection
(INTP)
0xFF
0xFF
0xFF
0x7F
0x7F
0x7F
Output Rate
Selection
(RATE)
0x5
0x4
0x3
0x5
0x4
0x3
Table 19. TBS Impulse Characteristics
from CS4373
Pulse Width
500 µ s
250 µ s
500 µ s
1 ms
2 ms
1 ms
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.
17.8 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.
(TBSGAIN)
Gain Scale
0x04B000
0x04B000
0x04B000
0x04B000
0x04B000
0x04B000
Factor
from CS4373
Pulse Height
~ 860 mV
~ 820 mV
~ 820 mV
~ 820 mV
~ 820 mV
~ 820 mV
CS5378
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