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PCM1794A: PCM1794A

Jahongir Dodokhonov
Prodigy 130 points
Part Number: PCM1794A
Other Parts Discussed in Thread: OPA1612, OPA1622, INA1620

Dear TI Team,

I want to clarify some points with PCM1794A DAC typical connection given in Figure 23 and 24 of the datasheet and ask some other related questions.

1. If I want to pull down pins 1,2,3,10,11,12 to ground, do I have to tie them with resistor or it can be tied to ground directly? What resistor nominals should be used if tied with resistor? What pins are allowed to be tied directly and which should be tied with resistor?

2. In Figure 23 and 24 of the named datasheet, DAC outputs are connected to "Differential to Single Converter With Low-Pass Filter" inputs directly and there's no resistor or simple RC filter installed in between them. Is it OK to follow the schematic provided in datatsheet ? 

3. In SBAA333, SBOA237 and TIDU672c documents given some usefull schematics which use OPA1612 and OPA1622 opamps for I/V and Differential to SE Stages. My question is if I use those schematics and opamps recomended, will they provide sufficient output power to feed the 16-32 Ohm headphones or I will have to add another stage after OPA1622 as an amplifier?

Best regards,

  • 0
    Prodigy 130 points

    I also want to add one more related question, which I forgot to post.

    If instead of OPA1622, INA1620 is to be used and taking into account that it has internally integrated 1K precision resistors that I want to use, what would be the optimal schematic in this case. I would like to know the capacitor and resistor nominals for the schematic where INA1620 is used.

    Here is the one as an example taken from TI tidu672c document.

    https://ibb.co/WDSNb56

  • +1 in reply to Jahongir Dodokhonov
    TI__Guru 52663 points

    Hi Johongir,

    1. These can be connected directly to GND, but generally I recommend 0Ω resistors to be used so you can potentially modify the state of the pin if you need to modify the design.  For example, connect FMTx to GND and VCC with 0Ω resistors, but only populate the resistor to GND.

    2. Yes, you can follow that schematic.  The differential-to-single ended converter that we show in the document also functions as a low-pass filter.

    3. I think the OPA1612 might be a bit low current for 16Ω headphones, but you can simulate if it is sufficient.  The OPA1622 would be a great choice for the final stage to drive headphones.

    The main issue with using the INA1620 is that the gain of the output stage will not be adjustable.  This circuit has best noise performance when you maximize the gain in the transimpedance stage and then use the final stage to attenuate the value to what you want for your headphones.  You can use the INA1620, but you will have to reduce the gain of the transimpedance stage to be your final output voltage.  This will increase the noise in the system and probably compromise the SNR and DR of the PCM1794A.

    I recommend the OPA1622 over the INA1620 on the final stage.

    Thanks,

    Paul

  • 0
    Prodigy 130 points

    Dear Paul_Frost,

    Sorry for late reaction to your reply. I would like to add some comment or correction to the 3rd part of my question.

    What I was meaning with "add another stage after OPA1622 as an amplifier" is to add additional amplifier after OPA1622 shown in the schematic as U2 and if there is a need for that. Will the original schematic without INA1620 as Headamp be enought to drive 16 ohm headphones. The schematic I was refering to looks like this.