Application Information

SPI OPERATIONAL DESCRIPTION

The serial data bits are organized into a field which contains 16 bits of data defined by TABLE 1. Bits1&2 determine the output

mode of the LM4921 as shown in TABLE 2. Bits 7 through 11 determine the volume level setting as illustrated by TABLE 3. Bit

12 sets the Bypass capacitor charging time.

Table 1. Bit Allocation

BIT #

Default Val

Function

Description

0 (LSB)

0

RESET_B

RESET_B = 0, Resets the DAC

Must be high for the part to run.

10

MODE CONTROL

See Table 2

20

3

0

MASTER/SLAVE

0 = SLAVE, 1 = MASTER

4

0

RESOLUTION

0 = 16 bit,1=32bit

5

0

RESERVED

Should always be set to ’1’

6

0

ZERO CROSSING SET

0 = ZXD ENABLE,1=ZXD

DISABLE

7

0

VOLUME CONTROL

See Table3-Volume Control

Settings

80

90

10

0

11

0

12

0

BYP CHARGE RATE

0 = 1X,1=2X

13

0

RESERVED

14

0

RESERVED

15 (MSB)

0

RESERVED

Should always be set to ’0’

MODE CONTROL

Sets the modes as outlined in Table 2.

Table 2. Output Mode Selection (Bits1&2 above)

Output Mode #

BIT 2

BIT 1

MODE

00

0

SD

1

0

1

STANDBY

2

1

0

MUTE

3

1

1

ACTIVE

Shutdown turns off the part completely for maximum power savings. The Standby mode turns off the clock but still consumes

more power than the shutdown mode. However, coming out of standby mode allows the part to turn back on faster than from

shutdown. In Mute mode the clocks remain on which uses more power but allows faster recovery and the ability to supply clock

signals to other devices which is important when the part is used in master mode. Active mode turns the part on for normal

operation.

MASTER/SLAVE SELECT

Allows the part to act as a master and supply the clock for

the rest of the system or be a slave to the system clock.

RESOLUTION SET

Sets the resolution to be either 16 or 32 bits of stereo audio

information. For most applications this will be set at 16 bits.

ZERO CROSSING DETECT SET

This pin turns on the zero crossing detection circuit. With this

circuit enabled the part will not allow a volume step change,

or shutdown mode, or standby mode to occur until the audio

input signal passes through zero. This pin should be set to

on for most applications.

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