Cirrus Logic CS492 Series, Manual

CDB4923 CDB49300

DS262DB2

17

8. OUTPUT

8.1

Analog Output

The six discrete outputs provided on the
CDB4923/300 are driven by CS4340 D/A convert-
ers. They can be found at RCA jacks J13-J16, J18,
and J20. Each output is driven directly by the
CS4340 to provide a 3.5 V

pp

 full scale output. The

CS4340 and its control signals can be found in Fig-
ure 11, and the analog output buffers can be found
in Figure 12.

The digital input format of the CS4340 is config-
ured using switch S4. The CDB4923/300 is
shipped with the CS4340 in I

2

S mode, and should

not be changed unless the CS492x/CS493xx has
been configured to use a different serial format.
The list of data formats for the CS4340 can be
found in Table 16. For more details on the features
of the CS4340, please reference the CS4340
datasheet.    

8.2

Analog Output Protection Circuitry

The CS4340 is designed to perform a ‘soft’ ramp-
ing of the bias voltage in order to prevent popping
on the outputs.  However, the series capacitance
found in the analog buffers of the CS4340 require a
finite amount of time to discharge when the
CS4340 goes into reset (RC time constant).  If the
full reset period is not observed before new audio is
delivered, popping can occur on the outputs. Please
see the CS4340 datasheet for more details.

The four transistors connected to the mute output of
each CS4340 are used to ensure that no 'popping'
will occur on the outputs during power-up, power-

down, and during audio clock discontinuities if the
reset period is violated. 

8.3

Digital Output

The signals present on analog outputs J13-J16, J18,
and J20 can also be found on the digital outputs
J45-J47 (AOUTDIG0-AOUTDIG2). The optical
transmitters are driven by CS8404A S/PDIF trans-
mitters (U19-21). The CS8404As are configured to
operate in consumer mode by default. The mode of
operation and status bits can be controlled by in-
stalling a 16 pin header in J44 and placing jumpers
on the signals that are to be programmed low. All
signals on J44 are pulled up by default. The
CS8404A transmitters and optical outputs can be
found in Figure 13.

The digital input format of the S/PDIF transmitters
can be controlled with switch S2 as listed in
Table 17. More operational details for the
CS8404A can be found in the CS8404A datasheet.    

Optical transmitter J43 (XMT958) is directly con-
nected to the S/PDIF transmitter of the DSP. It can
be used to directly observe the digital output of the
CS492x/CS493xx when the application code run-
ning on the part utilizes the transmitter. Note that if
the application code does not support S/PDIF trans-
mission, J43 will not generate valid data. Please see
the application note associated with the code in
question (e.g. AN120-123, AN140, or AN161-
AN163) to determine whether J43 should be active.

27DIF1

27DIF0

Digital Input Format

LO

LO

16-24 Bit I

2

S  (default)

LO

HI

16-24 Bit Left Justified

HI

LO

24-Bit Right Justified

HI

HI

16-Bit Right Justified

Table 16. CS4340 Digital Input Formats (S4)

M2

M1

M0

Audio Serial Port Format

LO

LO

LO

FSYNC & SCK Output

LO

LO

HI

Left/Right, 16-24 Bits

LO

HI

LO

Word Sync, 16-24 Bits

LO

HI

HI

Reserved

HI

LO

LO

Left/Right, I

2

S  (default)

HI

LO

HI

LSB Justified, 16 Bits

HI

HI

LO

LSB Justified, 18 Bits

HI

HI

1

MSB Last, 16-24 Bits

Table 17. Digital Input Format settings

 for CS8404A (S2)