TPS65131 - more power - Page 1
Forum section: electronics / projects

author: Skimask
author_rank: Super Contributor
timestamp: February 04, 2016, 04:50:20 pm
content: TPS65131 boost/inverting Positive & Negative DC-DC converterBuilt up the reference circuit in the datasheet for the evaluation module (TI datasheet # SLVU119C, page 8,http://www.ti.com/lit/ug/slvu119c/slvu119c.pdf), replaced the Vref divider resistors with trimmers. Circuit works well enough. With a good 18650 on the input, I can get +15v @ ~350mA (~20mV ripple) and -15V @ ~250mA (35mV ripple) all day.....or at least until the battery goes flat.I want more power.With reference to the internal block diagram of the TPS65131 (TI datasheet # SLVS493D, page 8,http://www.ti.com/lit/ds/slvs493d/slvs493d.pdf), I'm trying to come up with a way to add external pass FETs to parallel the internal switches and increase the total current capacity of the unit.Attempting some SPICE action now...

author: rx8pilot
author_rank: Super Contributor
timestamp: February 04, 2016, 05:04:36 pm
content: How are you going to parallel the FETs?Sent from my SAMSUNG-SM-G890A using Tapatalk

author: Skimask
author_rank: Super Contributor
timestamp: February 04, 2016, 05:13:09 pm
content: Aye...thar be the kicker...Maybe parallel isn't the way to put it. How about "in concert with" ? Maybe?The block diagram shows an internal N-channel switch for the + half, P-channel switch for the - half.With respect to the functional diagram on page 8 of the datasheet, I'm trying to figure out a decent way to hook up the INP and INN pins to drive the gates of a couple of external FETs...offload the switching (and the resulting thermals) to a pair of external FETs.

author: rx8pilot
author_rank: Super Contributor
timestamp: February 04, 2016, 05:59:49 pm
content: Boy that sounds super tricky if it is even possible at all. It's hard to image that it would not destroy the stability of the loop. Unless you have access to the gate pulses, it seems like a lost cause. Why not just get an external switch controller and make a new design?With that said, I have tried weirder things.

author: Skimask
author_rank: Super Contributor
timestamp: February 04, 2016, 06:28:26 pm
content: Worst case, it'll end up being a failed thought experiment.Probably won't work anyway. Like you said, wreck any built-in stability.As it is now, the IC is on a homemade QFN-DIP adapter (with lots of grounds), sitting on a homemade PCB. Isn't pretty, but it worked the first try. And with a 12V post-regulator on both rails, the final output is very clean (at least as clean as I can see on my Tek2446 and OwonSDS7102 with BWL off). Haven't put a SpecAn on it though. Don't know if I want to. Maybe just keep myself stupid happy as it is.

author: rx8pilot
author_rank: Super Contributor
timestamp: February 04, 2016, 07:21:20 pm
content: I have learned some of my most valuable lessons chasing 'bad' ideas. Since I am largely self-taught, I have a tendency to go after things that a classically trained EE might avoid because they were told that its not the right way. Sometimes I blow stuff up and sometimes I discover something new that I was told would never work. For me, one victory is worth a hundred or more 'failures'.

author: Skimask
author_rank: Super Contributor
timestamp: February 05, 2016, 08:08:42 am
content: Well, after a few hours of playing around in SPICE and the Falstad Circuit Simulator, I give upTime to find me another method...@rx8pilot - same here, self taught, unencumbered by the usual academic limitations. In other words, don't know what don't work until I don't try it.