Power supply suggestions for powering 3.3V audio processor from supply rails of TDA7293

[ravindra]

Hello,

I am using +/-40V to power TDA7293 and have no issues with its application.

I want to power an audio processor from the +40 supply rail. The audio processor needs 3.3V.

Kindly suggest a scheme to achieve this.

I am concerned about the power dissipation in the 3.3V regulator and power sequencing.

I would like to retain using the mute/stby ckt of the amplifier.

Thanks in advance!

Ravindra.

[Peter BENSCH]

This will likely depend on the current that's being drawn on the 3.3v rail, which regulator you should be using:

• a linear regulator could be used if the burned power is below 1W, which results in max 25mA and some heat sink to get the heat out of the package
• a DCDC regulator (SMPS) with better effiency, e.g. L7983 (max 300mA), L78987L (max 2A), L4976 (max 1A)

Power sequencing is probably not needed and too expansive (to switch Vs of the amp), but you could design some circuitry to hold stby/mute low while the DCDC converter starts up.

Regards

/Peter

[ravindra]

Hello,

Thank you for your early reply.

The 3.3V load can reach in the excess of 2.25W, so I was looking at L4973 and now the L4976.

I want to ensure that during power-down, the audio processor does not shut down first before the TDA7293 mutes. This along with the power dissipation of the step-down/ buck regulator is the problem I am trying to solve.

I could use L4973 (5.1V) or L4976 (5.1V) switching regulator powered from the amplifier rail and use this to power the 3.3V linear regulator with a small heat-sink. The 5V supply can also be used to power a relay (to switch the speaker) and its driver circuitry for late relay- ON and fast relay- OFF.

I need an opinion whether the above mentioned approach is any better than using an auxiliary transformer winding to generate a 5V (for relay driver circuit and relay) supply using a linear regulator. The 3.3V (audio processor) can be generated from the 5V.

Thanks!

Ravindra.