CS35L00

DS906PP1

17

“Electrical Characteristics - FSD Mode” on page 11, “Electrical Characteristics - HD Mode” on page 12, or

“Electrical Characteristics - FHD Mode” on page 13 for this value.)

page 9 for this value.)

5.3

Output Filtering with the CS35L00

The CS35L00 is specifically designed to minimize radiated electromagnetic interference (EMI) signals. All

of the devices are capable of meeting all stated data sheet performance numbers with no special filtering

required. Additionally, the device has shown to be below the compliance limits of both FCC and CISPR test-

ing with no external filtering required.

Ultimately, compliance with any radiated emissions requirements depends significantly on the entire system

under test. In applications where system-level trade-offs, such as compromised component layout or

lengthy speaker wires, have increased emissions levels, a passive output filter can be added to the outputs

of the device in order to decrease EMI levels.

5.3.1

Reduced Filter Order with the CS35L00

In applications which require an output filter, the unique design of the CS35L00 allows a much smaller,

less expensive output filter to be used than what is normally found in Class D amplifiers. In contrast to a

second order filter implemented with a series inductive element (traditional inductor or ferrite beads) and

a shunt capacitive element, basic filtering for the CS35L00 is accomplished by a single-order capacitive

element attached to the OUTx terminals. This is highlighted in Figure 5 below. Of course, if the system

requires more aggressive filtering, a ferrite bead can be added in series with the outputs to further atten-

uate system level noise.

5.3.2

Filter Component Selection

Usually, the need for output filtering is determined after the system under test has failed EMI testing. Dur-

ing this testing, problem frequencies are easily identified by the peaks which appear in the spectral plots

gathered in the EMI testing.

present a very low impedance at the frequency corresponding to the tallest peak in the spectral plot. If

present a very high impedance at the frequency corresponding to the tallest peak in the spectral plot.

Careful attention should be paid to the current carrying capabilities of any included ferrite beads and the

impedance of the ferrite beads in the audio band. A proper trade-off in ferrite bead selection is one that

CS35L00’s Minimized Optional Filtering

OUT+

OUT-

x

x

OUT+

x

Figure 5. Optional Output Filter Components