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Old 9th August 2004, 02:00 PM   #1
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Default PowerPad and the ultra extreme headphone amp TPA

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.

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.
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Old 9th August 2004, 02:26 PM   #2
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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...

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Old 9th August 2004, 02:41 PM   #3
Electrons are yellow and more is better!
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Jan, I have read this but if you would actually do the pcb, how would it look like? I have some problems to convert this text into a real life pcb.
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Old 9th August 2004, 02:42 PM   #4
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Hi P-A,

I have some here too, I'll test them soon.
As a preamp.
Numbers are impressive, but let's see (listen) how it sings.
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Old 9th August 2004, 02:49 PM   #5
Electrons are yellow and more is better!
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Quote:
Originally posted by carlosfm
Numbers are impressive, but let's see (listen) how it sings.
I have good (compared to others!) experience with current feedback amps so I have high hopes on this IC.
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Old 9th August 2004, 03:05 PM   #6
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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.

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Old 9th August 2004, 03:13 PM   #7
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This seams like the trend now at TI.
It's like reading a DIR1703 datasheet.
Clear as water.
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Old 9th August 2004, 03:26 PM   #8
Electrons are yellow and more is better!
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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?
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Old 9th August 2004, 03:35 PM   #9
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This is a new product, maby they will release an appnote with PCB layout.
The engineers that are writing that appnote are still decritping the datasheet!
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Old 9th August 2004, 03:44 PM   #10
Electrons are yellow and more is better!
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It's indeed . 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.
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