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PCB layout grounding for LM4766 application

Daniel Almeida
Expert 1010 points
Other Parts Discussed in Thread: LM4766

Hello everyone,

I'm projecting a PCB layout to use with an LM4766 application, the problem is that I want to use a dot bar display (with LM3915) and an amplifier for headphones, and I want to have all the circuits (LM4766, LM3915 and headphones amplifier) with distinct PCBs.

All the circuits need to have the same ground potential as the input signal, which can come from an RCA or 3.5 mm jack input, from CD player, TV, DVD, Blu-Ray and other devices.

I don't know if I can connect the input ground (reference) source to the power supply ground (which is in a separated PCB) as happens with all the other PCB circuits, speakers and headphones to form a star ground point.

The speakers can also be connected to the star ground point at the power supply, near the large filter capacitors?

I'm using in each PCB a very wide conductor with two reservoir capacitors and then I connect "power ground" of the ICs to this common point, which is directly connected to power supply ground.

I have no PCB experience can anyone help me?

I'm afraid of wasting money and time doing a PCB layout with signal injection on common (gnd), this problem sometimes happens with the breadboards I'm using making hums and sometimes the signal of the speakers is heard in the headphones with the input potentiometer of headphones amplifier in "cut" position .

I can send some PCB layouts to show what I'm talking about if it's necessary.

Thank you very much for your support,

Best regards,

Daniel Almeida

  • 0
    TI__Expert 3840 points

    Hi Daniel,

    The clean input reference ground will have to connect back to the main system ground where your reservoir caps are, however, many times there is a small resistance added between the two points for isolation or there is a small track pulled off the reservoir star point so that the clean reference ground is not corrupted by high charging currents or return currents. 

    Key goal is to keep high-return currents from the amplifier away from sensitive low-level signal grounds.

    All low-level signal grounds on different pcbs will have to connect back to the main system ground, otherwise the circuitry will be floating.

    A really good source for this info would be: http://www.douglas-self.com/ampins/ampins.htm

    This book specifically is extremely good: http://www.douglas-self.com/ampins/books/book.htm

    Best of Luck,

    JD

  • 0 in reply to John De Celles
    Expert 1010 points

    Thank you very much for your fast reply, which was very helpful,

    The gnd connection of LM4702C and LM4766 are high or low current?

    I think that this gnd connections are low current and only have the porpuse to put the amplifier with the same reference as the input.

    Best Regards,

    Daniel Almeida

  • 0 in reply to Daniel Almeida
    TI__Expert 3840 points

    Hi Daniel,

    You are correct. The ground connections for those ICs are low-level signal grounds and should reference the input.

    JD