TPS40211 design - Page 1
Forum section: electronics / projects

author: Mat219
author_rank: Contributor
timestamp: April 28, 2020, 09:07:01 pm
content: Hello.I'm working on an adjustable boost converter with TPS40211 and I have a few design questions about it:1)How can I make the output voltage adjustable without screwing the compensation up?2) Is it even necessary to have the compensation in the first place?3) If I do need a compensation, is there some easy way of choosing the values for it?Keep in mind I don't have a lot of spare components laying around so getting the values by experiment is not an option for me.Thank you for your time.

author: thm_w
author_rank: Super Contributor
timestamp: April 28, 2020, 09:31:37 pm
content: Instructions to calculate compensation are in the datasheet:https://www.ti.com/lit/gpn/tps40211You should probably have it, if its an issue, find another part which is internally compensated. The datasheet mentions series RC is the simplest option. If you are building a PCB, then add footprints for all three components.Can also use webench to calculate it:https://webench.ti.com/power-designer/switching-regulator/customize/7?noparams=0What I would do is pick the comp for the specific voltage you expect to be operating at most of the time. Then build it up and see if its stable at other voltages.Another method might be to check the lowest and highest output voltages, then pick a value within that range.

author: Mat219
author_rank: Contributor
timestamp: April 28, 2020, 10:01:21 pm
content: Thanks.I'll try that.One more thing.Here is the datasheet:https://datasheet.lcsc.com/szlcsc/1912281005_Texas-Instruments-TPS40211DGQR_C473356.pdfThe schematic on page 24, figure 8.2.1I think that i can replace R5 and R7 with a potentiometer for adjustable output voltage.Is that correct?

author: thm_w
author_rank: Super Contributor
timestamp: April 28, 2020, 10:28:19 pm
content: Yeah R5 and R7 divide down from Vout.You may need to add additional series resistors to limit the voltage you can select (say 40V maximum).

author: Mat219
author_rank: Contributor
timestamp: April 28, 2020, 10:32:41 pm
content: Okay. Thank you so much.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 28, 2020, 10:49:53 pm
content: Don't. This chip sucks.I haven't shopped for a replacement yet so I don't have a substitute unfortunately, but there are many similar offerings, shouldn't be hard to find another. Good luck,Tim

author: jbb
author_rank: Super Contributor
timestamp: April 28, 2020, 11:36:10 pm
content: Changing feedback resistor ratio will change the DC output voltage, yes. But it will also change the feedback gain, and thus change the response of the converter. So you’d need to check your compensation network works over the range of outputs you want.A better approach is to keep the feedback resistors fixed and inject somecurrentinto the feedback pin. This will vary the DC operating point without changing the gain, and might help with compensation design.Note that loop gain will change with duty cycle (ie output voltage) and whether the inductor is in continuous or discontinuous mode (ie output current).Also, that chip is kinda awful. Suggest you go for something with the switch built in. And maybe a diode or synchronous rectification.

author: TimNJ
author_rank: Super Contributor
timestamp: April 29, 2020, 12:04:04 am
content: Quote from: T3sl4co1l on April 28, 2020, 10:49:53 pmI haven't used the TPS40211 before. What's so bad about it?How about LM5022? I'm using LM5122 (the synchronous high-side MOSFET version) for a project, and it's been pretty straight-forward so far.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 29, 2020, 12:19:50 am
content: The fatal bug is that the overcurrent fault falls within the error amp's normal unsaturated range (2.2V or something).So it can't start up, as near as I can tell, ever. It just sits there trying to command full current, then chatters, resetting the soft start pin and waiting before doing it again.I had an application with 500mA 12V output; I got ~200mA startup current by removing the SS capacitor altogether. This makes it repeat at a few hundred us, which was enough to start up my application, but obviously not preferred.My thread on e2e, clearly not too happy discovering this:https://e2e.ti.com/support/power-management/f/196/t/751106Seemingly, they know it's a lemon and don't even support it!Yes, LM5022 should be reasonable. I haven't used it. Block diagram seems alright.Tim

author: SiliconWizard
author_rank: Super Contributor
timestamp: April 29, 2020, 12:42:00 am
content: Ahah, yeah: "Let me help you to get rid of all these troubles in a different way: we just released a new boost controller the LM5155, which is a better device that improves the current limit issues that you are facing."That's a really good one as far as support goes for this part

author: Mat219
author_rank: Contributor
timestamp: June 11, 2020, 12:30:33 pm
content: After a bit of research I settled on the LT3759.Now i just have to hope i designed the rest correctly.Which im not too confident about since this is my first design of any converter from scratch.Either way, thanks for the help everyone.