PowerPad and the ultra extreme headphone amp TPA

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peranders

peranders

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sjostromaudio.com
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#1
I have read the datasheet of TPA6120, slma004 and also slma002 .


Should I have a pad under the IC as described AND must it be connected or can it be left floating?

If I have a groundplane on the solderside, should I have a square hole in it so the normal pads have no groundplane underneath except for those mentioned?

Have I understood it right:
* Hole in groundplane, bigger than the IC

* Power pad on both sides with a couple of vias

* The powerpad connected to -12 V?

I have got samples and really want to test this current feedback amp. Technical data looks promising indeed. :nod:

The reason for I ask is that I have a great respect for 1300 V/us devices. I _may_ make pcb's but I'll start with a CAD design first. This will of cource be a SMD project and I will base it on QRV-04 but I think I'll will have regulators for each channel. This project is only for my own pleasure but I will make a couple of pcb's but this is _maybe_ in a few months.
 
#2
Per-Anders,

From the data sheet:

"Connect to ground. The thermal pad must be soldered down in all Thermal Pad - - applications to properly secure device on the PCB."

and:

"A ground plane should be used on the board to provide a low inductive ground connection. Having a ground
plane underneath traces adds capacitance, so care must be taken when laying out the ground plane on the
underside of the board (assuming a 2-layer board). The ground plane is necessary on the bottom for thermal
reasons. However, certain areas of the ground plane should be left unfilled. The area underneath the device
where the PowerPAD is soldered down should remain, but there should be no ground plane underneath any of
the input and output pins. This places capacitance directly on those pins and leads to oscillation problems. The
underside ground plane should remain unfilled until it crosses the device side of the input resistors and the
output series resistor. Thermal reliefs should be avoided if possible because of the inductance they introduce."

Seems pretty clear to me...

Jan Didden
 
#6
Per-Anders,

The only part that I think could be misunderstood is this:

"The underside ground plane should remain unfilled until it crosses the device side of the input resistors and the
output series resistor."

I interpret it that you leave the underside ground plane open under the device including the mentioned pins, because that is where you want to avoid capacitance. I would leave it open up to 5mm outside of those pins. I guess it would be OK to fill it under pins 6 to 15 (but also useless I guess). But you are right, the guy could have been a bit more specific.

Jan Didden
 
#8
One really confusing thing is that it's mentioned that "connect Thermal pad to ground"(page 5 in the datasheet). In the other document it's mentioned that the pad is always connected to most negative potential.

EDIT: This IC has a insulated pad which should be connected to ground. Obviously there are exception for how the PowerPAD is connected and this is not mentioned in the PowerPAD document. End EDIT.

The datasheet doesn't assume single supply. I'll supect a typing error on page 5.

Compare National and their switched regulators. They have very good and clear layout examples. When TI really emphasize the importance of good pcb layout, why don't they show it?
 
#10
It's indeed :flame: . The datasheet is from March 2004.

I notice also that they are not mentioning input bias current at all?😕 Page 14 mentions "... with a noninverting gain of -1 V/V". Some typos I'll guess.

What is the max input resistor value for noninverting mode?

Maybe this IC is totally unsuitable for unknown signal sources?

I did a quick measurement and the PowerPAD seems to be isolated from the rest of the chip but reserve myself in this. I may have tested only one polarity with the DMM.
 
#11
I just soldered the bottom to a solid copper wire and used it to attach to the perf board.

Chip didnt get hot at all.. maybe it depends on how you run it though.

Had a single 9V supply (wall transformer), and it seemed to clip if I turned my mp3 player to moderate levels..

Used the -2V gain setup..
 
#17
peranders said:
Thomas how much offset voltage did you get? Some values are mentioned in the document above but there are no figures in the datasheet (yet).

Do you like it? Does it deliver a "crisp" (according to TI) sound?
Click to expand...


I like it but its not quite powerful enough for my needs.

One measures .10V, the other I guess wrecked it somehow and it measures 1.2V

Didnt really spend a lot of time on them, so there was a bit of interference, but it was very quiet.

Sound was good as far as I could tell..
 
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