VS1003 connecting to amplifier

Designing hardware that uses VLSI Solution's devices as slave codecs such as an external MP3 decoder chip for a host microcontroller.
caffeine93
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VS1003 connecting to amplifier

Postby caffeine93 » Mon 2017-03-06 23:57

Hello everyone,

I'm currently designing a system which will use VS1003 to play out MP3 files on a 8Ohm speaker. The way I have connected everything is attached.

Vdd = 3.3V
Vcc = 2.8V

What I'm primary interested is connecting the output to the amplifier, the amplifier I use is mono amplifier TPA2005D1 (Datasheet: http://www.ti.com/lit/ds/symlink/tpa2005d1.pdf)

The inputs are defined in the datasheet as:
IN- Negative differential input
IN+ Positive differential input

My question is: are DC blocking capacitors needed since I did not put them in my design?

I read somewhere earlier than when connecting VS1003 outputs to the differential inputs of the VS1003, DC blocking caps should not be used and that the negative input should be connected to the GBUF output of the VS1003.

On the other hand, the following schematic on the link seems to have connected the DC blocking caps to the outputs of the VS1003 and reports that it works: http://www.pagemac.com/_media/projects/ ... p3_sch.pdf

So which one is the right way to connect it?

P.S. On my schematic, CS lines and RESET are not yet connected because I have not allocated my microcontroller pins to them yet :)
Attachments
VS1003_Connection.png
my VS1003 design
VS1003_Connection.png (45.96 KiB) Viewed 189 times

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Panu
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Re: VS1003 connecting to amplifier

Postby Panu » Tue 2017-03-07 9:13

Hi!

I think you should control the amp shutdown also with your MCU to avoid power-up pops from the speakers. And obviously you need the chip selects etc.

Please read the "MCU Howto" link below!

-Panu
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caffeine93
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Re: VS1003 connecting to amplifier

Postby caffeine93 » Tue 2017-03-07 14:55

Panu wrote:Hi!

I think you should control the amp shutdown also with your MCU to avoid power-up pops from the speakers. And obviously you need the chip selects etc.

Please read the "MCU Howto" link below!

-Panu


Thank you for the response.

I will make sure to connect both CS/RESET lines of the VS1003 and SHUTDOWN line of the TPA2005D1 to the MCU, thank you for the suggestion.

But the other thing I asked and am mostly concerned with is the DC blocking caps I asked about in my previous post?

Are they needed for the differential inputs of my amplifier? I did not put them on my schematic but the other design I linked in the previous post uses them?

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pasi
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Re: VS1003 connecting to amplifier

Postby pasi » Wed 2017-03-08 13:20

You don't need DC block because you are using differential input.

However, I would be wary of using resistor summing for the channels. Unless you also have simultaneous line output, I would use the differential output mode (SM_DIFF) and use LEFT as plus and RIGHT as minus for the AMP.

Also, you may need a low-pass before the amplifier to filter out-of-band sigma-delta noise. (See the line output connection for the low-pass.)
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caffeine93
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Re: VS1003 connecting to amplifier

Postby caffeine93 » Fri 2017-03-10 14:12

pasi wrote:You don't need DC block because you are using differential input.

However, I would be wary of using resistor summing for the channels. Unless you also have simultaneous line output, I would use the differential output mode (SM_DIFF) and use LEFT as plus and RIGHT as minus for the AMP.

Also, you may need a low-pass before the amplifier to filter out-of-band sigma-delta noise. (See the line output connection for the low-pass.)



Thank you for the suggestion.

I checked my schematic again and I think I already have the delta-sigma reconstruction stage (R30 + C30 and R32 + C33)?

So the way you are proposing is that I connect LEFT (after the delta-sigma stage) directly to PLUS and RIGHT (after the delta-sigma stage) directly to MINUS of the amplifier? In this proposed configuration, GBUF is not needed at all?

Also, SM_DIFF is a mode that is enabled by sending a write command from the MCU to the VS1003 in the initialization process?

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pasi
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Re: VS1003 connecting to amplifier

Postby pasi » Fri 2017-03-10 17:37

Yeah, you're right, the low-pass is there. ( ref viewtopic.php?f=9&t=69 )

In the differential connection GBUF would not be used. (LEFT and RIGHT have similar components and thus similar biasing time, so you may get less issues during power-up.)

SM_DIFF is the lowest bit in the SCI_MODE register. You would set it to '1' to activate the differential mode.
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