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DA7202

10 W Mono Class-D Amplifier for 2S Battery Devices

Company confidential

Datasheet

Revision 3a

20-Aug-2015

CFR0011-120-00 Rev 5

21 of 25

10 Application information

10.1 PCB layout

The performance of the DA7202 relies on good PCB layout. Failure to follow best practice can have

undesired side effects that include, but are not limited to, electromagnetic interference (EMI) and

electromagnetic compatibility (EMC) problems, ground bounce, and voltage losses. Poor layout can

also affect regulation and stability. Dialog Semiconductor recommend that the following guidelines

are followed:

● Place any input capacitors and output capacitors close to the device using short tracks. These

components carry high switching frequencies, and long tracks can act as an antenna.

● Maximise the size of ground metal on the component side to help with thermal dissipation.

● Use a ground plane with several vias connecting to the component side ground to further reduce

noise interference on sensitive circuit nodes.

● If external resistors are to be used to change the gain, these should be placed close to the

device.

● It is recommended that ferrite beads are included on the output paths to reduce EMI interference

and noise.

10.2 Speaker selection

The output from the DA7202 Class-D amplifier contains high frequency signals that are a result of its

switched PWM operation. These high frequency harmonics are at a much higher frequency than is

recommended for most speakers, so they must be filtered out to protect the speaker.

The correct choice of speaker is therefore important since the speaker itself can act as a low-pass

filter, attenuating the undesirable high frequency harmonics while still passing the desired audio

frequencies.

The 3 dB cut-off frequency for speaker inductance and resistance can be calculated using the

following formula:

fc = RLOAD / 2πL

Therefore to achieve a 3 dB cut-off frequency of 20 kHz with an 8 Ω speaker, a speaker should be

selected with an inductance of:

L = RLOAD / 2πfc = 8 Ω / 2π * 20 kHz = 64 μH

8 Ω speakers for portable applications typically have an inductance in the range of 20 μH to 100 μH.

Speakers with a higher inductance than the 64 μH calculated above will have a 3 dB cut-off

frequency below 20 kHz, resulting in a reduced audio bandwidth. Conversely, speakers with an

inductance lower than 64 μH will have a higher cut-off frequency.

DA7202 데이터시트(PDF) 21 Page - Dialog Semiconductor