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How to connect TPA6132A2 SGND and PGND

Robert Lewis
Prodigy 100 points
Other Parts Discussed in Thread: TPA6132A2, TPA6140A2

I have searched and read through the notes on connecting the SGND for the TPA6132A2 stereo amp and do not understand the correct connection.

The doc set specifies SGND as "Amplifier reference voltage. Connect to ground terminal of the headphone". But we have a four layer pcb with the center plane as GND. On any layout we do, the router directly connects the common on the headphone jack to GND and SGND to ground via a via at the closest point to each of these two signals. Therefore they are not directly connected to one another other than by the internal ground plane.

Should we manually run a trace from the common on the headphone jack to an island polygon SGND within the main GND plane and then use this separate ground plane as an isolated ground plane within the inner ground, and finally tie this 'island' ground plan to the main digital ground plane with a single trace? The entire board is digital with the exception of this amp.

Thank you for any suggestions and help.

Robert

  • 0
    Prodigy 130 points

    Robert,

    One of the key features of the DIRECTPATH headphone amplifiers is that they do not require the usual DC-blocking capacitors at the output. To define the zero DC output reference voltage, SGND is used as the ‘quiet’ reference ground for the amplifier feedback networks. Voltage disturbance of SGND will be translated directly to the amplifier outputs. The PGND of this part is used as the ’noisy’ ground to catch the transient currents associated with the HPVDD and HPVSS charge pumps.

    I would route the SGND, OUTR, and OUTL signals all together to the headphone jack where the SGND and headphone jack GND terminal would together both contact the board GND plane. 

  • 0 in reply to ROD
    Prodigy 100 points

    Rod

    I will follow your advice and connect these signals at a single point. Further to this I created a separate isolated ground plane within the main gnd layer and then connected the two gnds with a zero ohm resistor.

    Thank you for the help.

    Robert

  • 0 in reply to ROD
    Prodigy 50 points

    Is the SGND pin on TPA6140A2 different from the SGND on the TAP6132A2?

    I ask because the TPA6140A2 data sheet seems to indicate SGND should only be connected to the TRS shield ground, and not to the AGND.  Am I correct in assuming that SGND connected only to the TRS shield ground (and no other ground) is necessary for the "SGND Pin Eliminates Ground Loop Noise" functionality?