SM5846AP datasheet(35/36 Pages) NPC

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SM5846AP

NIPPON PRECISION CIRCUITS—35

Serial data format

Address information is displayed in double-line cells of the table.

Test bits (mode ﬂag 1 bit 4 and mode ﬂag 3 bit 6) should be set to 0.

System Reset

When a reset is necessary

The device must be reset under the following condi-

tions.

When power is ﬁrst applied

When the LRCI clock or system clock stop

Reset input conditions

The RST input is active LOW.

At power-ON reset, RST must go LOW and then go

HIGH after the XTI and LRCI clocks stabilize (reset

release).

Reset timing

The internal arithmetic registers and output sequence

are initialized on the rising edge of the LRCI clock

after reset release. The internal control ﬂags and D-

ATT attenuation register are initialized after RST

goes LOW. Outputs DOL and DOR are tied LOW

while RST is LOW.

Power-ON reset using a capacitor

The RST input conﬁguration is a Schmitt-trigger

input with a pull-up resistor, which means that a sim-

ple power-ON reset circuit can be made by connect-

ing a capacitor between RST and VSS as shown

below.

A 0.01 µF external capacitor is recommended. How-

ever, the time constant can be lengthened if longer

time is required for the XTI and LRCI clocks to sta-

bilize after power-ON.

The external capacitor discharges through the inter-

nal pull-up resistor at power-OFF as this is the only

possible discharge path. This could cause reset fail-

ure if power is reapplied while the external capacitor

is discharging. Therefore, a diode should be con-

nected between RST and VDD to quickly discharge

the capacitor and ensure correct power-ON reset

operation.

External power-ON reset circuit

Bit 1

Bit 2

Bit 3

Bit 4

Bit 5

Bit 6

Bit 7

Bit 8

D-ATT attenuation

Mode ﬂag 1

SYNC

TEST1 = 0

FSEL1

FSEL2

DEEM

Mode ﬂag 2

MUTE

DITH

OBS

IBS1

IBS2

Mode ﬂag 3

ASEL1

ASEL2

TEST2 = 0

‘

Internal Pull-up Register

External

Capacitor

Schmitt Buffer

RST

Discharge

for Diode

Internal Pull-up Register

Schmitt Buffer

External

Capacitor

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