CS5376A_05 Datasheet, PDF (66/108 Pages) Cirrus Logic – Low-power, Multi-channel Decimation Filter

CS5376A
Test Bit Stream Impulse Characteristics:
Interpolation
Selection
(INTP)
0xFF
0xFF
0xFF
0x7F
0x7F
0x7F
Output Rate
Selection
(RATE)
0x5
0x4
0x3
0x5
0x4
0x3
Pulse Width
from CS4373A
500 µs
1 ms
2 ms
250 µs
500 µs
1 ms
Gain Scale
Factor
(TBSGAIN)
0x04B8F2
0x04B8F2
0x04B8F2
0x04B8F2
0x04B8F2
0x04B8F2
Table 20. TBS Impulse Characteristics
Pulse Height
from CS4373A
860 mV
820 mV
820 mV
820 mV
820 mV
820 mV
Custom TBS Data
If a required test frequency cannot be generated us-
ing the on-chip test bit stream data, a custom data
set can be written into the CS5376A. The number
of data points to write, up to a maximum of 1024,
depends on the required test signal frequency, out-
put rate, and available interpolation factors. Cus-
tom data sets must be continuous on the ends; i.e.
when copied end-to-end the data set must produce
a smooth curve.
17.5 TBS Sine Wave Output
When the TMODE bit in the TBSCFG register is
low, the TBS generator operates in sine wave
mode. In this mode, sine wave data from digital fil-
ter memory is used to create a sine wave test signal
that can drive a test DAC. Sine wave frequency and
output data rate are calculated as shown by the
characteristic equation of Table 19.
The sine wave maximum ∆Σ one’s density output
from the TBS generator is set by the TBSGAIN
register. TBSGAIN can be programmed up to a
maximum of 0x04FFFF, with the TBS generator
unstable for higher amplitudes. For the CS4373A
test DAC, a gain value of 0x04B8F2 produces an
approximately full scale sine wave output (5 V_pp
differential).
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 calculated as shown in Table 20.
To create a -20 dB impulse from the TBS genera-
tor, the TBSGAIN register should be set to maxi-
mum 0x0078E5, and the INTP bits in TBSCFG
should also be set to maximum 0xFF. The RATE
bits should be set to produce data at the correct rate
for the 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 input
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 CS5376A test bit stream
generator is a feedback path to the digital filter
MDATA inputs. This loopback mode provides a
fully digital signal path to test the TBS generator,
digital filter, and data collection interface. Digital
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