SM5843A Datasheet, PDF (18/24 Pages) Nippon Precision Circuits Inc – Audio Multi-function Digital Filter

SM5843A×1
System Reset (RSTN)
The SM5843A×1 must be reset under the following
conditions.
s At power-ON.
s When the LRCI clock and internal operation tim-
ing need to be resynchronized.
s When switching the CKSLN clock select input.
s When switching between filter characteristics
using TMOD2.
s When either or both of the LRCI and XTI clocks
stop or are interrupted.
The system is reset by applying a LOW-level pulse
on RSTN.
The arithmetic and output timing counters are reset
on the first LRCI start edge after reset is released, as
long as the XTI clock has already stabilized. The
LRCI start edge is determined by the state of INF1N
and INF2N. When INF1N is LOW or when both
INF1N and INF2N are HIGH, the start edge is the
rising edge. When INF1N is HIGH and INF2N is
LOW, the start edge is the falling edge.
When RSTN is LOW, the DOL and DOR outputs are
LOW, muting the output signal to an attenuation
level of −∞.
The power-ON reset pulse can be applied by a
microcontroller or, for systems where XTI and LRCI
are stable at power-ON, by connecting a capacitor of
several hundred pF between RSTN and VSS. For
systems that do not use a microcontroller, the capaci-
tor must be chosen such that the XTI and LRCI
clocks fully stabilize before RSTN goes from LOW
to HIGH.
RSTN
LRCI
Internal reset
WCKO
1
2
DOL
DOR
Figure 6. System reset timing and output muting
Filter Characteristic Selection (TMOD2)
There are 2 digital filter frequency response charac-
teristics incorporated into the SM5843A×1, selected
by the state of TMOD2. A sharp roll-off characteris-
tic (response 1) is selected when TMOD2 is HIGH,
and a slow roll-off characteristic (response 2) when
TMOD2 is LOW. The response is modified by
changing the number of taps in the 1st FIR filter
stage, as shown in figure 1.
Dither Rounding-off Processing
(TMOD1)
Dither rounding-off processing of output data is ON
when TMOD1 is LOW. Dither is OFF and normal
processing mode is selected when TMOD1 is HIGH.
s Filter response 1
• 153-tap 1st FIR
• 29-tap 2nd FIR
• 17-tap 3rd FIR
s Filter response 2
• 25-tap 1st FIR
• 29-tap 2nd FIR
• 17-tap 3rd FIR
Note that the device should be reset when changing
TMOD2 during normal operation.
NIPPON PRECISION CIRCUITS—18