TPA3110D2 - pop noise

Hello Matsumoto-san,

Are you experiencing this pop while playing audio when you cycle SD?

If you cycle SD with audio playing, deepening on where in the input cycle the output turns on, there will be a discontinuity. For example, a SD event on the peak of an input sin wave will cause a transient voltage spike equal to the peak voltage signal across the speaker.
To minimize pop, it is always recommended to stop the audio signal before putting the device into SD.

Do you have any oscilloscope photos of the output noise during a SD event?

Best Regards,
Matt

Matsumoto san,

The changes made to the output filter including the inductor and the removal of C14 and R9 should have no effect on the pop performance.

If you are experiencing pop even without music playing, make sure that the input DC blocking capacitors have matched time constants. These capacitors are charged during power on to 3V and due to the differienal input of the amplifier, if the RC charge time of the INP and INN paths are different, pop will often be a heard.

If the time constant is similar, make sure low tolerance capacitors and resistors are used at the inputs. They should be 5% or better to insure that the charge time is the same on the negative and positive inputs.

Best Regards,

Matt

Matsumoto san,

I am happy to hear that your customer was able to track down the problem.

C14 and R9 are called a Zobel network. When driving a loudspeaker, due to the voice coil inductance, the impedance seen by the amplifier increases with frequency. This causes the Q of the output filter to increase and may case ringing and other issues. The C14/R9 Zobel will help flatten this out as its impedance falls at higher frequencies.

Zobels are also very common in speaker crossover design in a multi-driver speaker enclosure.

Best Regards,

Matt