TPA3144D2: Help me Calculate Ferrite Bead Value for this Amplifier

Hello Shashank! Thanks for your message and Shawn can help you out with your questions. There are some good guidelines that work in most cases as laid out in the datasheet under section 10.2.2.1 "Ferrite Bead Filter Considerations" where designers tend to just use the NFZ2MSM series from Murata. Also, section 10.2.2.3 "When to Use an Output Filter for EMI Suppression" also provides some very good information on what to use and when. Also, to help shown in answering further questions... what type of power supply and power input level are you planning to use & also what modulation scheme are you planning to use and what type of speaker load and output power are you intending to use in your design? Thanks, Jeff

Hi SHASHANK,

For the triditional class-D amplifier, LC output filter is needed because the switching waveform results in maximum current flow. The ripple current is large for the traditional modulation scheme, because the differential voltage swing is 2×VCC, and the time at each voltage is half the period. An LC filter with a cutoff frequency less than the class-D switching frequency allows the switching current to flow through the filter instead of the load. The filter has less resistance but higher impedance at the switching frequency than the speaker, which results in less power dissipation, therefore increasing efficiency.

The TPA3144D2 modulation scheme has little loss in the load without a filter because the pulses are short and the change in voltage is VCC instead of 2×VCC and the time at each voltage is shorter. Ferrite bead + capacitor filter is only used to supress EMI. It is important to select a ferrite bead that is effective in the 10 to 100 MHz range which is key to the operation of the Class-D amplifier. The impedance of the ferrite bead can be used along with a small capacitor with a value in the range of 1000 pF to reduce the frequency spectrum of the signal to an acceptable level.  Also, it is important that the ferrite bead is large enough to maintain its impedance at the peak currents expected for the amplifier.

Best regards,

Shawn Zheng

Hello Jeff,

We are like extremely new Audio, And ill try to answer what all i know

We have decided to use BD-modulation since our Speakers wire length is extremely small (5-6 cm)

We are planning to connect 2 speakers (Stereo) Left and Right each of 4 ohms. Refer to figure 25 in 10.2 in TPA3144D2 datasheet

Help me understand what do u mean by output power !!! 6 watts is what the amplifier can do at max right ?

Regards
Shashank

Hello Shawn,

We are giving 7v supply to an 2x4 ohm speaker!!!

Regards
Shashank