# SSM351

Hi there,

I am currently designing a 4ohm speaker to drive 5W rated, 10-15W peak using the SSM3515 amplifier and have some questions below:

a) What is the operating voltage range for the I2S and I2C lines? Can they operate on 3V3 level as my host processor are running at 3V3.

b) If we could operate at 3V3, then should I still configure to use both the internal 5V AVDD and 1.8V DVDD?

c) What is the optimum driving voltage for the amplifier to obtain the best performance (in terms of efficiency and current draw) for 5W rated, 10-15W peak speaker?

d) To drive the 4 ohm speaker at 5W rated power, based on 12V input supply with 85% eff, the audio amp will draw approx. 0.35mArms / 0.5mApeak? So we should take the peak current as the actual current draw from the supply, is my calculation and assumption correct?

Thanks,

HS

• Hi HS,

Here are the suggestions,

a. The I2S FSYNC and BCLK are compatible to 3.3V but SDATA pin is only 1.8V compatible. So for I2S I would suggest use 1.8Vp-p signals. The I2C can support 3.3V logic. Since the DVDD must be 1.8V it would be good if you could use 1.8V CMOS logic signals in the design.

b. The 5V and 1.8V both can be generated using internal regulator. The 5V is used by the internal Analog circuits and cannot be used for powering any external circuits. The internally generated DVDD of 1.8V also cannot be used to power external circuits.

c. For 5W RMS output power in 4ohm, the PVDD needed would depend on the THD+N desired. If 5W, 1% THD+N is ok then 7V PVDD would be enough. Use the plots in Datasheet for the 4ohm load. This would give close to 85% efficiency.

d. If using 12V with 4ohm for 5W rms output, then with 85% efficiency power supply current of 0.5A would be needed. But for peak power capability you might want to have some extra reserve capacity in the power supply.

Thanks

Rajeev

• Hi Rajeev,

Thanks for your reply. I will make changes to my design to have I2S signals at 1.8V while keeping the I2C at 3.3V.

Thanks & regards,

HS