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Class D Switching Power Amplifiers and Power D/A conversion

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Old 12th July 2014, 03:42 AM   #1
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Join Date: Jul 2014
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Hi,
I would like to preface this with i'm a software engineer, not an EE, but do dabble at the hardware level when writing device drivers. So please forgive my ignorance with some of my questions as when things go beyond the chip on an I2C or SPI bus, I'm a little out of my league.

I am wanting to make an amplifier for my car - replacing the factory head unit and putting in an amp that can be up to the size of a double DIN. An iPad would be mounted in front.

Here is a system overview:
Click the image to open in full size.

And the detailed audio:
Click the image to open in full size.
(I'm not sure why the images look stretched)

I found the evaluation board for the TAS5622A and a circuit for a 600 watt SMPS circuit.

My plan would be to use JL Audio C5-650's which are 4 ohm nominal with 75 watt RMS and 225W peak.

SMPS Questions
  1. The data sheet for the TAS5622A says the typical voltage used is 32.5V. Does each parallel section with the LM5122MH in it contribute both voltage and current in the boost? e.g. since there are 4, do each contribute 6V and 6.25A?
  2. If the voltage scales linearly with the number of parallel contributors and I get it to 36V, would i use an LDO to bring it back down to 32.5V? The data sheet says a max of 34V for the TAS5622A.

Amplifier Questions - TAS5622A
  1. The data sheet shows it been used with a Class-G power supply. Does the PMP7969 circuit fit this class? If not, does it even matter?
  2. I currently have my diagram with 4 amplifiers configured as mono PBTL. Is there any need for this configuration with the speakers I have chosen? This would halve the amplifier components.

I don't have any preference to using TI components - it's when I was googling for things, they seemed to be the first results. Would these components be a good selection?

I know I'm currently swimming in the deep end of the pool, but I'm reading as much as I can each day trying to breakdown my electronics ignorance and gain a better understanding of the task at hand.

If anyone can provide feedback would be greatly appreciated.

Thanks,
Greg
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Old 13th July 2014, 04:56 PM   #2
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Join Date: Dec 2003
Location: Munich
PSU:
The internally paralleled phases of the PMP7969 are all delivering the full 24V, but just a fraction of the output current.
Changing the PMP7969 to 32V would need a change of the internal loop control network in best case and might additionally need to change the inductors in worst case...
Furtheron matching SMPS with audio amplifiers is always difficult, because audio amplifiers draw heavily modulated power with max levels which are double of the rated amp power, while most SMPS are not designed to delivery double power for short term. So if you are chosing a SMPS which is not specifically designed for audio, you will need an oversized SMPS.

Fortunately at 24V the power of the TAS will be less, it should be fine to power your four chanels from one PMP7969 with 24V.
Regulation behavior of the PMP7969 seems to be pretty OK - it is likely to work without catastrophic side effects.


[QUOTE=ghulands;3988669]
The data sheet shows it been used with a Class-G power supply. Does the PMP7969 circuit fit this class? If not, does it even matter?
[/QUOTE
PMP7969 is not class G.
However I do not find any proposal or requirements for a class G supply in the TI documentation. Just the need of an additional 12V for the USB board.


Quote:
Originally Posted by ghulands View Post
I currently have my diagram with 4 amplifiers configured as mono PBTL. Is there any need for this configuration with the speakers I have chosen?
If you want to power the amps with more than 15V then stay with PBTL.
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