Hello,
I plan to develop my own board to convert a USB flow to a SPDIF flow, because the "ready to use" boards cannot be easily integrated in my other designs. The highest possible quality is the goal of course.
I have read this old post, but it is 15 years old (!) and it is closed.
I only need to generate a SPDIF output for the classic 16bits/44.1kHz CD format, because I only lesson to this format, and I will convert this SPDIF flow to a ST optical output to feed my Wadia 9 DAC. (if higher rates are possible, why not, but it is not mandatory).
So it seems to me that the PCM2906 is an option (the CM6631A looks complex and requires a firmware configuration tool), but maybe you have newer recommendation ??
Question 1: According the PCM2906 datasheet available here., the attached Figure 36 shows that a Power Supply at 3.85V, whereas I would expect 3.3V: what is the explanation ?
Question 2: As I plan to only use the SPDIF output, I can probably ignore the pins 15 and 16, and consequently C11 and C12 can also be ignored. The pins 12 & 13, respectively VinLeft and VinRight can probably also be ignored.
I will appreciate your replies,
Thank you very much,
I plan to develop my own board to convert a USB flow to a SPDIF flow, because the "ready to use" boards cannot be easily integrated in my other designs. The highest possible quality is the goal of course.
I have read this old post, but it is 15 years old (!) and it is closed.
I only need to generate a SPDIF output for the classic 16bits/44.1kHz CD format, because I only lesson to this format, and I will convert this SPDIF flow to a ST optical output to feed my Wadia 9 DAC. (if higher rates are possible, why not, but it is not mandatory).
So it seems to me that the PCM2906 is an option (the CM6631A looks complex and requires a firmware configuration tool), but maybe you have newer recommendation ??
Question 1: According the PCM2906 datasheet available here., the attached Figure 36 shows that a Power Supply at 3.85V, whereas I would expect 3.3V: what is the explanation ?
Question 2: As I plan to only use the SPDIF output, I can probably ignore the pins 15 and 16, and consequently C11 and C12 can also be ignored. The pins 12 & 13, respectively VinLeft and VinRight can probably also be ignored.
I will appreciate your replies,
Thank you very much,
1. It's a high performance application circuit, and I think they are overruling the internal 3.3 V regulator by applying a slightly higher external voltage: almost 4 V minus a Schottky diode forward voltage drop. Presumably the recommended external regulator is better than the internal one, and the higher voltage gives the ADC and DAC a bit more voltage headroom. The Schottky diode prevents disasters when the internal regulator starts up faster than the external one.
2. Sounds logical to me.
2. Sounds logical to me.
Regarding point 1: I agree with you , the external voltage regulator should be better than the internal one.
On the schematics of the Figure 36, as you say, the output voltage should be 4V minus the Schottky diode drop to reach 3.86V.
But when I look at the recommended REG103xA-A Voltage Regulator, it exists only in 3.3V or 5V fixed output, so this let me think that they use the Adjustable version (suffix A-A).
The datasheet is available here: https://www.ti.com/lit/ds/symlink/reg103.pdf
and the figure related to the adjustment is in the 1st page:
I assume that Vin is +5V (maybe 9V or 12V would be better), so what values do you recommend for R1 and R2 in order to get Vout=4V ?
Maybe a trimpot for one of these resistor would allow a more precise setup ?
Thank you
On the schematics of the Figure 36, as you say, the output voltage should be 4V minus the Schottky diode drop to reach 3.86V.
But when I look at the recommended REG103xA-A Voltage Regulator, it exists only in 3.3V or 5V fixed output, so this let me think that they use the Adjustable version (suffix A-A).
The datasheet is available here: https://www.ti.com/lit/ds/symlink/reg103.pdf
and the figure related to the adjustment is in the 1st page:
I assume that Vin is +5V (maybe 9V or 12V would be better), so what values do you recommend for R1 and R2 in order to get Vout=4V ?
Maybe a trimpot for one of these resistor would allow a more precise setup ?
Thank you
OK MarcelvdG, so I design my board with these values.
According to this figure 37 of the PCM2906 datasheet, the PCM2906 itself is powered by the "Vbus" pin (through a 2R2 resistor), and the REG103A is also powered by the Vbus pin, meaning the USB positive voltage ( +5V), so I suppose that +5V is enough to power the REG103A.
According to this figure 37 of the PCM2906 datasheet, the PCM2906 itself is powered by the "Vbus" pin (through a 2R2 resistor), and the REG103A is also powered by the Vbus pin, meaning the USB positive voltage ( +5V), so I suppose that +5V is enough to power the REG103A.
Apparently.
Why do you go for the high-performance application circuit of figure 37 rather than the simple one of figure 39? Chances are that only the ADC and DAC that you don't use behave differently.
Why do you go for the high-performance application circuit of figure 37 rather than the simple one of figure 39? Chances are that only the ADC and DAC that you don't use behave differently.
It is possible, but not sure: maybe the chip will perform better (with a good VR) on the SPDIF conversion, even when the DAC conversion is not use...
And I will design a PCB that will also allow the full usage of the PCM2906, even if I don't use it in a first time...
I used the EVM design without issue. There is a cheaper tpaxxx regulator that’s equivalent to the reg103.
If you loopback spdif, you can record your audio stream.
If you loopback spdif, you can record your audio stream.