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Class D Switching Power Amplifiers and Power D/A conversion

TAS5825M based amp
TAS5825M based amp
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Old 27th March 2019, 09:21 AM   #21
Firerunning is offline Firerunning  China
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Join Date: Mar 2019
Quote:
Originally Posted by lutkeveld View Post
If you send your requirements I can export a complete header file for you.
My requirements are:Process Flow 8 (Housekeeping, 2.0),up to 192kHz,32bit audio process,Hybrid Modulation,BTL Mode(2.0 Channel), PWM frequency set to 768 kHz and Class D bandwidth set to 175kHz,PVDD Tracking / Thermal Foldback disable,others are set by default.

Quote:
Where did you get it from?
I get the header file from a post on e2e audio forum
Question of TAS5825 Audio Format Support in PPC3
Although it was not what I really wanted, it still helped me a lot.
By the way,I found some necessary registers in the TAS5805M datasheet,which is exactly the same as the TAS5825M.

Best regards,

Firerunning
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Old 27th March 2019, 12:22 PM   #22
lutkeveld is offline lutkeveld
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Join Date: May 2013
Here is a header file dump of the Housekeeping flow that is already:
-Set to 32 bit data
-Set to hybrid modulation, Fsw=768khz and bandwith=175khz

The header file contains example code on how to write the settings to the device in C. Change to .h instead of .txt before use.

I used this way of setting the DSP on a custom PCB with atmel processor. In my case there was a small catch:
The array is big, so it needs to be placed in flash by adding 'const PROGMEM' before the arrayname. After that if you want to read the contents back you have to use 'pgm_read_byte_near'.

I don't know the specifics for your micro, you have to figure that part out yourself.
Attached Files
File Type: txt Housekeeping.txt (4.5 KB, 8 views)
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Old 28th March 2019, 08:42 AM   #23
aurel32 is offline aurel32  France
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I am a bit concerned by the power dissipation on the PCB. Would it make sense to use this circuit in dual mono, using 2 chips in PBTL mode (even for 8 ohm loads) in order to spread the heat dissipation on 2 chips?
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Old 28th March 2019, 08:51 AM   #24
Firerunning is offline Firerunning  China
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Join Date: Mar 2019
@lutkeveld
Thank you for the header file provided. I tried to configure the amplifier based on the header but failed. After I set it to BD Mode and deleted the DSP coeffs,the amplifier work again. I found that the coeffs can not be written in. This is a mystery.
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Old 28th March 2019, 10:56 AM   #25
lutkeveld is offline lutkeveld
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Join Date: May 2013
@Aurel32 I would not be too concerned when you are playing music. If you listen to sinewaves it might be troublesome. PBTL would be better for heat dissipation but doubles idle current, component cost and board space.

@firerunning Please confirm that the chip acknowledges all commands and writes the whole array. It should work, I suspect you have something wrong in your I2C write functions.
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Old 21st April 2019, 08:25 PM   #26
aurel32 is offline aurel32  France
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@lutkeveld
Thanks a lot for the feedback, this was enough to decide myself to build an amplifier based on this chip. I have chosen to build it as a form of an Raspberry Pi Hat:


tas5825m-based-rpi-amp.jpeg


So far I have only tested it with a 12V power supply, I have already ordered a 24V power supply with sufficient output power. It works and sounds great, it's incredible how such a small chip can output so much power with so good quality. It's a big change from my DAC + preamp + Mosquito amplifier in 19" enclosures for basically the same performances.

The TAS5825M is used with a 10H/680nF output filter. I used the same Murata inductors as in the EVM. The PVDD power supply is bypassed with 2x680F + 2x10F ceramic + 100nF ceramic per channel. It uses a 2 layer PCB board, and the bottom layer almost consists in a ground plane, which I hope will be sufficient for power dissipation. I'll have to wait for the 24V power supply to test that. The 3 GPIO outputs are connected to 3 LEDs, the TAS5825M can be configured to display various information (fault, warning, automute, etc.).

I am used to solder chips with an exposed pad and with leads using a reflow station and flux but without stencil. I have applied the same technique for the TAS5825M, basically as shown there: YouTube. It was however less easy than expected, the surface tension was not so important as with a chip with leads, and thus I had to align it perfectly during the reflow. Nevertheless I have been able to solder it correctly.

The board also contains a 5V 3A DC/DC converter based on a LMR33630 chip to backpower the Raspberry Pi. It also features an LTC4365 DC input protection to protect the board from wrong polarity (as it can happen with this style of jack), under or over voltage. Mouser ran out of stock between the moment I passed my order and it got prepared, so I have not solder that part yet. I'll do that when I receive it in the next days. Finally the board also hosts a 24LC32 EEPROM to meet the Raspberry Pi HAT specification.

I have designed the board using Kicad. In the next weeks, I plan to change a few minor issues I noticed on the current board (like silkscreen, via diameter) and release the design in an opensource license.

On the software side, as an amateur I do not have access to PPC3. I therefore used the Housekeeping.txt sequence from @lutkeveld to initialize the TAS5825M. The chip is capable of way more things, I'll look at that later. Right now I am using a small Python code using py-smbus, but I plan to write a proper kernel driver at some point.
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Old 22nd April 2019, 01:19 PM   #27
lutkeveld is offline lutkeveld
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Board looks great! I was also thinking about a hat PCB, but you beat me to it. Its a shame that TI's software is not more open.

Reverse polarity protection can also be done with a simple P-channel mosfet:
Reverse voltage protection with a P-FET | Hackaday
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Old 22nd April 2019, 01:35 PM   #28
aurel32 is offline aurel32  France
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Quote:
Originally Posted by lutkeveld View Post
Reverse polarity protection can also be done with a simple P-channel mosfet:
Reverse voltage protection with a P-FET | Hackaday

I agree, that said the circuit there is doing more than reverse polarity protection, it also disconnects the load if the voltage is too high (I set the limit at 28V) or too low. Powering it with a too low voltage (that could be due to current protection) will leave the Raspberry Pi in a bad state and can corrupt the SD card.
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