Audio Codec info on STM32f469-Disco

[ashutoshr]

I'm using a STM32F469i- discovery board for developing a prototype & would like to use the Audio DAC feature in it and it is given in the datasheet that one set of pins (15 & 16 in CN12). I checked this discovery board's and also the controller's datasheet but were unable to find any information regarding the resistance of the speaker that can be connected to the pins. Will this pins(15,16 in CN12) be able to comfortably drive a 8 ohm speaker, having watt-rating less than 1 W? Would love to get some insights on this

Cheers, Have a great day

[SofLit]

Hello @ashutoshr and welcome to the community,

This something related to the codec itself so need to refer to the CS43L22 datasheet.

According to its document:

For more details you can contact the Codec manufacturer "Cirrus Logic".

[waclawek.jan]

No.

No pin on STM32 is to be loaded by an 8Ohm load, but with those pins, things get even "worse".

I haven't looked at what are pins 15&16@CN12, but I assume you are talking about the DAC output pins, PA4 and PA5.

[EDIT] This was an incorrect assumption, thus rest of my post is moot; see next posts of this thread. [/EDIT]

In fact the DAC has a relatively high output impedance, read datasheet. You can have an internal buffer switched off or on, but even with the internal buffer the output impedance is far higher than needed to drive directly a speaker. And, you can also damage the DAC, if you overload it or abuse in any other way (e.g. ESD).

In other words, you need an audio amplifier. One solution could be to use something like PC speakers.

JW

[SofLit]

He's talking about the on board audio codec output:

[ashutoshr]

This STM32 series has an audio DAC

[SofLit]

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@ashutoshr wrote:

This STM32 series has an audio DAC

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No. STM32 doesn't have Audio DAC (only regular DAC) but some boards have audio codec on board as STM32f469-Disco board. For this board, it's the CS43L22 from Cirrus Logic. Some of its outputs are mapped on CN12/pins 15 & 16.

[ashutoshr]

Oh so, since this STM32 disco board is already having a Audio codec, I can directly plug in the speakers to the mentioned pins(CN12- pins 15 &16), and from the Datasheet you have shared earlier, I can see that I can connect a 4 ohm speaker having a rating of 1W, one small clarification I have you have underlined those 2 details because the voltage provided on those pins are 3.7V (which gives the Vrms to be roughly 2.5V, right) ?

So, in conclusion if I have understood it rightly, if I connect a 4 ohms speaker, rated with a power of 1W, I can safely drive the speaker using only STM32f469  since it has a audio codec integrated.

Thanks for your quick response

[waclawek.jan]

> He's talking about the on board audio codec output:

I stand corrected. Thanks.

JW

[SofLit · Accepted solution]

@ashutoshr 

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if I connect a 4 ohms speaker, rated with a power of 1W, I can safely drive the speaker using only STM32f469  since it has a audio codec integrated.

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According to the following graph I dressed which is based on the data of the datasheet, you can connect 4 ohm speaker but at 3.3V you cannot exceed ~850mW (by interpolation).

In any case, you need to contact Cirrus Logic for confirmation as its the IC manufacturer: https://www.cirrus.com/support/

Hope I answered your question.

[ashutoshr]

Oh I see, Duly Noted. One more small clarification, so that I can ask the people at Cirrus logic clearly, the output we are talking about, i.e 3.7V this value is given(outputted) by the Cirrus logic codec, right?

so what voltage value is provided by the pins 15 & 16, I have to get it clarified from the Cirrus logic people and accordingly decide on the power and ohms? Or is te voltage provided by the STM32 and it is 3.7V for this particular STM32f469 disco board