Design guidelines for PCB schematic and layout

AN4015

14/22

Doc ID 022507 Rev 1

6

Design guidelines for PCB schematic and layout

6.1

Schematic

6.1.1

Main driver for the selection of components

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is suggested.

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Coil saturation current must be compatible with the peak current of application

6.1.2

Decoupling capacitors

There are two different ways to use the decoupling capacitors:

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The decoupling capacitor(s) can be shared among channels; the layout must be

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One decoupling capacitor can be used for each channel. It is mandatory that each

decoupling capacitor be placed as close as possible to the IC pins. This solution is

implemented on the TDA7498E demonstration board.

6.1.3

Output filter

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Snubber network: the key function of a snubber network is to absorb energy from the

inductive component in the power circuit (the output coils and the speaker). The

purpose of the snubber RC network is to dissipate the unnecessary high pulse energy,

such as a high voltage spike, in the power circuit which is dangerous to the system.

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Main filter (low-pass filter): The purpose of the main filter is to remove the carrier

frequency (

≈310 kHz) and to cut off the frequency higher than the audible range of

20 kHz. The LPF filter is implemented by a passive Butterworth topology. In order to

have a clean and flat frequency response, it is mandatory to design the filter to fix the

cutoff frequency a little bit above 20 kHz.

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Damping network: The purpose of the damping network is to avoid the high-frequency

oscillation issue on the output circuit. When the load is disconnected from the amplifier,

the frequency response of the main filter is not flat and there is the possibility of adding

gain in a frequency band. The damping network also improves the THD performance.

The damping network can also avoid the inductive effect of the PCB tracks when the

system is working at high frequency with PWM.