PCM510xEVM-U
Table 1. PCM510xEVM-U Headers, Test Points, Jumpers, and Switches
(continued)
Connectors/Switch/Jumper/Test Point
Description
J4
Optical S/PDIF Input
J5
Coaxial S/PDIF Input
J6
BNC External MCLK Input
Switches
SW1
EVM Reset
SW2
Select EVM Application
SW3
MCLK Select
LEDs
D2
RX Lock
D3
SRC Ready
2.5
Clock Circuitry
SW3 allows for MCLK selection from multiple sources. The PCM510xEVM-U contains an external BNC
jack, J6, as well as one programmed oscillator that provides a clock frequency of 24.576 MHz. The
TAS1020B also provides a MCLK output; by default, this clock is used as the master clock for the
PCM510xEVM-U. Depending on the application requirements, the SRC4392 is also able to derive a
received clock output (RCKO) output based on the input clock frequency, and this derived clock output
can be used as the MCLK input for the PCM510x as well. This option is enabled by setting a shunt in
position 1-2 (RXCKO) on the 3-pin jumper W5. If W5 has a shunt in position 2-3, then setting SW3
determines which MCLK source is used, as summarized in
Table 2. SW3 Clock Selection
Setting
A
B
C
Onboard MCLK from
Low
Low
Low
TAS1020B
External MCLK 3.3-V
High
Low
Low
BNC Input
24.576-MHz MCLK from
High
High
High
PLL Y3
2.5.1
MCLK Source Matching
The SRC4392 is equipped with two audio serial data ports, each of which generates BCLK and LRCLK
signals. When the SRC4392 receives an S/PDIF input, it automatically derives the MCLK of the input,
which is sent to the RXCKO pin. Dividers are used to send the generated BLCK and LRCLK from the
audio ports (if they are in master mode). For certain use cases, the SRC4392 is set up so that these ports
are used. When routing through the audio serial ports on the SRC4392, it is important to use RXCKO as
the master clock source for the PCM510x. In order to ensure proper operation, the master clock source
must be synchronized to the bit and word clock supplied to the PCM510x. Therefore, the master clock
source for the PCM510x must also be replicated from the digital input source, which is why RXCKO must
be chosen. If the master clock source for the PCM510x is the onboard MCLK from the TAS1020B USB
controller, for example, then there is potential for synchronization mismatch between the master clock
supplied to the PCM510x and the bit and word clocks being supplied to the PCM510x. For use cases
routing through the SRC4392 audio serial ports, look to jumper W5 for selecting RXCKO as the master
clock source, as opposed to one of the options chosen by adjusting SW3. The
has additional routing information.
The PCM510x devices contain an internal PLL and BCLK reference, so that the MCLK can be generated
internally. When using external I
2
S input directly into the W3 jumper, a MCLK can be derived form the
BCLK input. Refer to the PCM510x product data sheet for more details.
6
PCM510xEVM-U
SBAU190A
–
May 2011
–
Revised June 2011
Copyright
©
2011, Texas Instruments Incorporated