DS913DB2

7

CDB35L00-X4

2. GROUNDING AND POWER SUPPLY DECOUPLING

The CS35L00 requires careful attention to power supply and grounding arrangements to optimize performance and

minimize radiated emissions. The device decoupling capacitors should be located as close to the CS35L00 as pos-

sible. This can be optimized by using both top and bottom side component population as demonstrated by the

CDB35L00-X4 board.

2.1

Power Supply Decoupling

Proper power supply decoupling is one key to maximizing the performance of a Class-D amplifier. Figure 5

and Figure 6 on page 11 show the component placement for the CDB35L00-X4 board. Note the addition of

the C13, C23, C33, and C43 capacitors connected to the LFILT+ pin. This pin is used as decoupling for the

internal LDO regulator when operating in HD or FHD modes.

The small value decoupling capacitors are placed as close as possible to the power pins of the CS35L00

on the CDB35L00-X4 board. It is recommended that the power supply decoupling capacitors reside on the

opposite side of the board from which the CS35L00 is populated on. This allows for very close placement

of the decoupling capacitors to the power supply pins of the CS35L00 without interfering with the differential

audio inputs or differential audio outputs. This placement keeps the high-frequency current loop small to

minimize EMI.

2.2

Electromagnetic Interference (EMI)

This reference design is a board-level solution that is meant to control emissions by minimizing and sup-

pressing them at the source, in contrast to containing them in an enclosure.

2.2.1

Suppression of EMI at the Source

Several techniques are used in the circuit design and board layout to minimize high-frequency fields in

the immediate vicinity of the high-power components. Specific techniques include the following:

• As mentioned in Section 2.1, effective power supply decoupling of high-frequency currents and mini-

mizing the loop area of the decoupling loop is one aspect of minimizing EMI.

• Differential input and output signals should be routed differentially whenever possible.

• A solid ground plane on the adjacent PCB layer underneath all high-frequency traces to minimize the

loop area of the return path.

• Optional output EMI filter component landings are available as described in Section 1.7.1, if emissions

need to be further reduced.

• Keeping the switching output filter components as close to the amplifier as possible.