TPA3255: SE to Diff Input Stage Star Ground

Hi,

I think you can keep the 15->12V power supply as PGND. And on the op-amp side, use AGND. Then connect the PGND and AGND with a ferrite bead.

This will keep all the signal chain refer to the AGND, while the power supply related ground as PGND.

Does it make sense for you?

Thanks!

Regards,

Sam

Hello, Sam! Thanks for quick response. I think i got it. I has redrowed my picture to make sure i understood you correct, can you please look at it? Since we already have one connection (AGND->PGND) inside a chip itself, If i connect AGND plane and PGND plane elsewhere with a ferrite bead isn't it like crating GND loop? 

Regards,

Vasiliy

Hi,

Single point A/PGND connection should be used to avoid GND loop, so no need to add a ferrite bead as you already have one to connect the A/PGND together.

Thanks!

Regards,

Sam

Well thank you. Then I want to clarify for the last time whether I understood correctly. So, to achieve the best result:

1. "50-15 V DC-DC" supply should seat at PGND plane as "15-12V" one.

2. 12V_OA(for OPAMPs) and VMID grounds goes straight to AGND point near chip by separate wires. (Or it is enough to lead only the ground of VMID supply with a separate wire and leave 12V_ОА anywhere on the AGND?)

3. All input's AGND shoul go with separate wires to AGND point near chip and OPAMP's AGND can pe placed anywhere at AGND plane due opamp high PSRR.

4. Inner connection inside TPA3255 from AGND pins (12, 13) to PGND pins (25, 26, 33, 34, 41, 42) is necessary and sufficient for connect AGND to PGND at whole PCB.

Regards,

Vasiliy

Hi Vasiliy,

Regarding 2, I think it is enough to lead only the ground of VMID supply.

Regarding 4, please make sure a 0R resistor or ferrite bead connection is used between AGND and PGND on PCB.

Thanks!

Regards,

Sam

Hello, Sam! I apologize for my meticulousness, and I hope I do not take much of your time. I got your point regarding 2, but I am at a loss about 4. Are pins 12, 13 and 25, 26, 33, 34, 41, 42 not connected inside the TPA3255 chip?

My idea is to connect AGND plane and PGND plane directly through the chip, as shown in the picture. At lefthand side of PCB I have separate AGND plane and at the righthand side I have separate PGND plane. There is no connection between two planes until I place TPA3255 at PCB. At lefthand side of TPA3255 we have AGND pins 12 and 13 and at righthand side we have PGND pins (25, 26, 33, 34, 41, 42). So, placing chip at its location connects AGND and PGND planes together through the chip at ONE location. If these contacts are already connected inside the chip, then no additional connections can be made so as not to create an GND loop (as in the figure above). Or are these contacts not connected inside the TPA3255? Could you give a little more detailed comment on this question, please?

Regards,

Vasiliy

God bless TI! Thank you Sam! You helped me a lot, thanks for the technical support! Good luck to you!

Regards,

Vasiliy