Is it viable to power TPA6120A2 from single Li-ion cell? - Page 1
Forum section: electronics / beginners

author: ov_darkness
author_rank: Contributor
timestamp: December 03, 2016, 02:25:45 pm
content: Hi all!I come from Poland. I'm sorry excuse of engineer (no formal education in this direction whatsoever).I like to fix and build things, especially audio electronics.I'm trying to design as small as possible (http://www.hammondmfg.com/pdf/1455C801.pdf) headphone amplifier, that could be powered from USB and Li-ion cell (specifically 18650).Similar projects in the past where almost entirely Cmoy (Chu Moy's) deisgn derivatives, powered from the ancient 6F22 (9V). Even the legendary NwAvGuy used them!There are some really cool production headamps out there (e.g. Fiio A5), but I wan't to flex my design muscles a bit on this one, so I've decided to complicate this task as much as possible.First, I want to use TI's TPA6120A2 headphone chip. It can take +/-5V to +/-15V voltage.But the case size constraints (it has to fit on the back of the smartphone) doesn't allow for 2x18650 power source.Why Li-ion?Best Ni-MH 6f22 on the market has about 2.5Wh of capacity. Best 18650 is above 12Wh.Even with average 80% efficiency there will be still ca. 4 times more juice available.So I have only two options:1. boost 3.7V to let's say 12V and use rail splitter circuit. I think that it will be less power efficient, but will also take less space.2. use 2 separate converters to make positive and negative 6V rails.Which one is better? Or maybe something else entirely?I'm going to add TP4056 li-ion charger with safety chip, cause there's no protection IC on my 18650's.Another problem is volume control, because I find potentiometers not elegant enough, expensive, and bulky.I'd really appreciate your thoughts on the topic.

author: Zero999
author_rank: Super Contributor
timestamp: December 03, 2016, 06:45:29 pm
content: Why have you decided to go for the TPA6120A2?How about using an IC designed to run off a lower power supply voltage? Then there would be no need for a boost converter.

author: Zero999
author_rank: Super Contributor
timestamp: December 03, 2016, 07:17:23 pm
content: If the headphones are not very sensitive, and you really need a large voltage swing, then what about using a voltage doubler, run at the same rate as the audio frequency?I don't know who well it will work, as C1 and C2 take awhile to charge, which could cause some distortion for a short length of time, after an increase in music volume.

author: ov_darkness
author_rank: Contributor
timestamp: December 04, 2016, 11:12:58 am
content: I chose that IC because I have functioning PCB with it and I could use it to prototype my amplifier.TPA6120 doesn't require many parts on PCB so it should be fairly easy to make small PCB with it.Also I don't know another die with comparable performance. It's used in some really good sounding devices.

author: Zero999
author_rank: Super Contributor
timestamp: December 05, 2016, 11:26:23 am
content: To answer the original question. It's possible to use the TPA6120A2 on a single supply rail, by DC biasing it so the inputs and outputs are at half the supply voltage and AC coupling the parts of the circuit, which should be at 0V, to the negative or positive supply rail.As you're using a switched mode power supply, you'll need to pay a lot of attention to screening the inductor and filtering the output. The power supply rejection of the TPA6120A2 decreases, as the frequency increases and at higher frequencies, there's a risk of demodulation, causing a horrible noise to be transmitted to the headphones.I think you should still consider a lower voltage IC. I doubt the TPA6120 gains you much, once you've factored in the extra complexity of a boost converter and the associated filtering to minimise noise.There are plenty of headphone ICs which will work directly from 3.3V to 5V, see links below:http://www.ti.com/lit/ds/symlink/tpa6130a2.pdfhttp://www.ti.com/lit/ds/symlink/tpa6135a2.pdfhttp://media.digikey.com/pdf/Data%20Sheets/NXP%20PDFs/TDA8559_3.pdfhttps://datasheets.maximintegrated.com/en/ds/MAX9722-MAX9722B.pdf