CS35L01/03

18

DS909A2

allows the ferrite bead to sufficiently attenuate the problematic high-frequency emissions without compro-

mising audio performance.

5.3.3

Output Filter Power Dissipation Considerations

In systems without inductive series elements like inductors or ferrite beads, power losses in the output

filter are equal to the switching losses that occur in the system due to the cyclical charging and discharging

of capacitors connected to the amplifier outputs. In systems that require an inductive series element, con-

ducted losses also occurs due to the series impedance added to the output path.

5.3.3.1

Conduction Losses for All modes of Operation

For all modes of operation (SD, FSD, HD, and FHD) of the CS35L01/03, the conduction losses are gov-

erned by the equation:

Where:

P

= Power dissipated in the series impedance.

I

= RMS AC output current

Z

= impedance of the series element at the frequency of the AC current

This equation neglects any series impedances presented by the PCB traces or speaker wires in the output

path.

5.3.3.2

Switching Losses in SD/FSD Mode

Switching losses in SD/FSD Mode are governed by the equation

Where:

P

= Power dissipated in the capacitor (neglecting parasites).

C

= Value of filtering capacitor

V

= Peak voltage developed across the capacitor

f

= Switching frequency of the outputs

These calculations are straightforward, as the peak voltage is simply the voltage level attached to VBATT,

the capacitor is the value of capacitor that has been added for filtering (neglecting parasitic board capac-

itances), and the frequency is 192 kHz or 76 kHz for SD and FSD, respectively.

5.3.3.3

Switching Losses in HD/FHD.

Many factors affect the switching losses when the device is operated in HD/FHD mode. These factors in-

clude the frequency of the content being amplified, the voltage level of VBATT, and the amplitude of the

output signal will factor into both the voltage presented across the capacitors and the frequency at which

the capacitors are charged or discharged.

=

P

1

2

=