Cirrus Logic CRD35L01 - Manual (Page 6)

6 DS914RD2
CRD35L01
2. GROUNDING AND POWER SUPPLY DECOUPLING
The CS35L01 requires careful attention to power supply and grounding arrangements to optimize performance and
minimize radiated emissions. The decoupling capacitors should be located as close to the CS35L01 as possible.
This can be optimized by using both top and bottom side component population as demonstrated by the CRD35L01
boards.
2.1 Power Supply Decoupling
Proper power supply decoupling is one key to maximizing the performance of a Class-D amplifier. Figure 6
and Figure 7 on page 10 show the component placement for the CRD35L01-SD board. Figure 18 and Fig-
ure 19 on page 12 shows the component side placement for the CRD35L01-HD board. Note the addition of
the C8 capacitor 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 CS35L01
on the CRD35L01 boards. For the WLCSP package it is recommended that the power supply decoupling
capacitors reside on the opposite side of the board from which the CS35L01 is populated on. This allows
for very close placement of the decoupling capacitors to the power supply pins of the CS35L01 without in-
terfering with the differential audio inputs or differential audio outputs. This placement keeps the high-fre-
quency current loop small to minimize power supply variations and EMI. These capacitors are not required
to be expensive low-ESR capacitors.
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.