Dear TI audio IC designers,
We need in TPA6120 headphone amplifier additional information:
There is power supply capacitance of low ESR 100uF electrolytic on each rail at the TPA6120A2 headphone amplifier datasheet application circuit.
There are such power supply capacitors on the TPA6120A2 Evaluation Module schematic (slou169 document).
Unfortunately, the TPA6120A2 Evaluation Module user’s guide has no information regarding its real THD specification.
Is it enough the TPA6120A2 power supply capacitance of those low ESR 100uF on each rail to keep the headphone amplifier THD value (in full sound bandwidth range) at the datasheet listed level and load resistance of 70..300 Ohms?
The TI audio forum (in the Audio FAQs ) has some considerations on this subject:
How can I improve low frequency THD+N in my design?
If you changed PVDD capacitance, you can see increase THD+N at low frequency input case and also this value depends on channel separation factors. If someone would like cost reduction by decreasing PVDD cap value and size, should check low frequency vs THD+N spec before changing capacitance.
Just wanted to mention a few things: My QRV07 headphone amp using the TPA6120 is one of the most popular designs I have made and it works pretty good. There has been no troubles whatsoever building it. I used TI's recommendation of 18 vias under the chip.
My soldering tips for an amateur:
Put fresh tin under the PowerPad
Solder pin 1 and 7 (important that one side is soldered. Now the IC will have their opposite pins in the air.
Turn around the pcb and let the TPA6120 be against the table.
Heat up the soldering iron to max. Apply tin at the 18 via holes on the solder side and pressure the pcb against the table. Notice when the tin on the PowerPad is starting to melt and the IC is moving closer to the pcb. You don't have to worry about by now the really hot pcb.
Solder the rest of the pins.
18 via holes under the TPA6120
There only dumb answers, not dumb questions ... right? Just want to double check with you on three things.
1. The input resistance to TPA6120 is 300 KOhms, so the 50 ohm in series at the input of the noninverting pin AND any
other additional resistance to the left of Rs will add up to be the "Input Impedance" right? In my case my colleague want to add 4.7Khoms to the left of Rs to increase the input voltage to at least 10Vpeak with out producing clipping at the output AND without triggering thermal shutdown if a constant tone is supplied at the input for a length of more than 4 mins.
2. The total load impedance should count: 10 ohms (Ro) + Load Impedance + 10 ohms (Ro) if the circuit uses each Amp handles one side of a truly matched (differential input) or it should only include the Ro + Rload ?
4. Are there any heat sinks that any of you would recommend just to provide additional protection if someone drives the amp at max input for a sustained (continuous) length of time?
Sal, I am very happy to hear about the success you have had with your design. I will try to answer these new questions.
I expect you refer to the schematic you sent long ago, "harpy_b1_schematic.pdf".
1. Input resistance to the circuit is the 50ohms to the left of the noninverting input in series with the parallel combination of the 4.02k to ground from there and TPA6120A2 non-inverting input impedance. Circuit gain is reduced by the loss in the resistor divider these parts form.
You can increase the value of the 50ohm resistor or add more resistance in series, and this will increase the divider loss, so the input can be increased without causing clipping.
2. The total load impedance does consist of Ro and Zload, and there is loss from the divider that these form.
3. I think you will be able to find a small heatsink from Aavid (http://www.aavid.com/), Wakefield (http://www.wakefield.com/) or a number of other heatsink vendors by visiting their websites or looking on Digikey (http://www.digikey.com/) under "Fans, Thermal Management / Thermal - Heat Sinks".
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