AN400

Rev. 0.5

5

R11 (25

to 2 k) is a required series termination resistor when using digital audio output (Si4741/43/45 only) and

is used to mitigate noise from the digital frame clock routed to DFS pin 18. The recommended value of the resistor

is 1.4 k

 for optimal edge rate and noise suppression. Confirm that timing requirements are met with the selected

series termination resistor value. Place R11 as close to the host controller as possible.

R22 and R23 (4.02 k

) are optional pull-up and pull-down resistors for the RCLK line to reduce the energy in

harmonics of RCLK that might fall in the AM band. The recommended value is chosen such that RCLK will still

meet the voltage requirements of Si474x. Place R22 and R23 as close as possible to RCLK pin 11. If the RCLK

frequency is higher than the maximum frequency in the AM band, this will eliminate harmonics of RCLK that fall in

the AM band. Refer to “AN332: Si47xx Programming Guide” and “AN344: Si4706/07/4x Programming Guide” for

recommended RCLK and prescalar values.

R2 (24.3 k

) and R13 (4.53 k) are optional pull-up and pull-down resistors for the DFS line when using digital

audio output (Si4741/43/45 only.) They are used to reduce the energy in harmonics of DFS that might fall in the AM

band. The recommended value is chosen such that DFS will still meet the voltage and timing requirements of I2S.

Place R2 and R13 as close as possible to DFS pin 18.

2.2. Si474x 4x4 mm Schematic

Figure 1. Si474x 4x4 mm QFN Schematic