SM5843AS1 datasheet(18/24 Pages) NPC

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SM5843A

×1

NIPPON PRECISION CIRCUITS—18

System Reset (RSTN)

The SM5843A

×1 must be reset under the following

conditions.

At power-ON.

When the LRCI clock and internal operation tim-

ing need to be resynchronized.

When switching the CKSLN clock select input.

When switching between ﬁlter characteristics

using TMOD2.

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.

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.

Filter response 1

• 153-tap 1st FIR

• 29-tap 2nd FIR

• 17-tap 3rd FIR

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.

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.

Figure 6. System reset timing and output muting

RSTN

LRCI

WCKO

DOL

DOR

Internal reset

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