Cirrus Logic CS35L32 - Manual (Page 33)

DS963F4 33
CS35L32
5.3 External Component and PCB Design Considerations—EMI Output
To avoid the current transient on the VP node, the boost converter management must be configured for a fixed 5-V boost
operation (VBOOST_MNG = 11) before issuing a flash event. VBOOST_MNG may be reconfigured to the desired
management mode after a flash event.
The following sequence should be followed when issuing a flash event:
• Configure VBOOST_MNG to fixed 5-V Mode (VBOOST_MNG = 11).
• Trigger a flash event by asserting FLEN.
• Wait for the expiration of the flash timer period.
5.3 External Component and PCB Design Considerations—EMI Output Filtering
In a portable application, it is important not only to pass far-field radiated emissions compliance testing such as FCC
Part 15 or EN55022, but to minimize near-field emissions. In general, far-field compliance testing ensures that an
electronic device does not interfere with other electronic devices. Also, near-field emissions are more of a concern when
ensuring that an electronic device does not interfere with itself. As the name indicates, near-field emissions typically do
not propagate far enough to interfere with another device.
Depending on system characteristics (e.g., PCB layout, stack-up, supply decoupling, the connection length to the load,
presence of external shielding, sensitivity of other devices on the system, and proximity to any sensitive devices or
antennas), an EMI reduction may be necessary over the performance of what is obtained with the typical connection
diagram (see
Fig. 2-1 ). Because most Class D amplifier emissions are produced or transmitted via the output stage,
changes are typically limited to adding passive filtering to SPKOUT+ and SPKOUT–. For sensitive systems, it is
recommended to add a ferrite-bead capacitor (FB-C) output filter to help ensure sufficient attenuation of the high-frequency
energy.
Fig. 5-1 shows recommended VMON and IMON connections where an FB-C output filter is used.
Figure 5-1. VMON and IMON Connections with FB-C EMI Filtering
5.4 PCB Routing Considerations for Thermal Relief
Due to the thermal dissipation properties inherent to a wafer-level chip scale package (WLCSP)—and because the
CS35L32 contains a boost converter, Class D amplifier, and LED driver, which can dissipate a fair amount of thermal
energy—the PCB design should account for how to remove heat from the device.
The simplest approach is to take advantage of as many GND ball locations as possible and connect them in a manner that
allows for good thermal conduction. For example, a 10-mil diameter, 6-mil drill through-hole microvia under each
nonblocking GND ball location would allow thermal energy to transmit through the PCB and reach the back-side surface,
where it dissipates most effectively. For reference purpose, GND balls are B5, C2, C3, C5, as shown in gray in
Fig. 5-2 .
Generic Simulated
Speaker Load
33 H R
SENSE
0.1 
8 
SPKOUT+
ISENSE+
ISENSE–/VSENSE+
SPKOUT–/VSENSE–
FB
OUT
FB
OUT
SPK+
SPK– C
OUT
C
OUT