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PCM3070: Questions regarding HP output

Robert Alfred Kecs
Prodigy 170 points

Part Number: PCM3070

Hi,

I am useing the PCM3070 s HP outputs single ended, i want to use LDOIN as HP power input in order to get a larger output voltage swing. There is no mention of this configuration but also no mention that it is not valid.

As for electrical caracteristics I assume Full scale output voltage (0dB) for singl eneded is 1/2 of the differential value. so about 0.889Vrms output? 
Is this corect? or are there other HW limintations that reduce this value ?

Should i set CM to 0.75V or 0.9V ? Page 1 / Register 10: Common Mode Control Register - 0x01 / 0x0A 

I think i should set CM=0.9 and Output Common Mode for HPL & HPR is 1.65V . 

Also can the HP output function in DC mode? In the typical aplication all outputs are AC coupled. I was wandering if i can use a HP output as a DC DAC in order to set a DC bias for a circuit. What abut the Line output? I can provide a HiZ input buffer, since i expect there is not that much DC current drive strenght if any.

What do you think about this usecase/aplication? 

Best regards,

Robert

  • 0
    TI__Guru 51140 points

    Hi Robert,

    The datasheet does mention this exact configuration and it is valid to use.

    There are also specs provided for the single-ended headphone mode.

    You are correct though that half of the differential value is the supported single-ended value. The full swing depends heavily on the output common mode chosen, which is why you see different FS values in the spec table.

    Robert Alfred Kecs said:
    I think i should set CM=0.9 and Output Common Mode for HPL & HPR is 1.65V

    This is fine. This will put your headphone common mode at half of the max LDOIN supply value. The input common mode setting of 0.9 doesn't really matter here since you will override it with 1.65V anyway.

    AC coupling is the intended application. I would not generally recommend DC coupling the headphones directly. If you want to send the signal to a external buffer you should use the line outputs instead since those are intended for higher-z loads like a buffer would be. This depends on what exactly you want to achieve with the output circuit, but in general I recommend keeping things AC coupled.

    Best regards,
    Jeff McPherson