Available nA Iq buck-boost converters ? - Page 1
Forum section: electronics / beginners

author: JL34
author_rank: Contributor
timestamp: May 14, 2022, 08:40:02 pm
content: Hello,I am looking for a nanoamps Iq buck-boost converter, like the TPS63900. No matter how much I look, I can't find stock.I know we are in Semiconductor shortage, but perhaps someone knows a place to find some ?Purpose is to generate 3.3V from a supercap (1V - 3.85V), with ultra low quiescent current.Thanks

author: Marco
author_rank: Super Contributor
timestamp: May 14, 2022, 09:10:43 pm
content: TPS61098DSER if you're quick.

author: PartialDischarge
author_rank: Super Contributor
timestamp: May 14, 2022, 09:45:38 pm
content: Bq25570, boards available on ebay

author: JL34
author_rank: Contributor
timestamp: May 15, 2022, 08:03:48 am
content: Thanks both for your reply.@Marco, TPS61098DSER could be the last solution. According todatasheet, it can output 3.1V on his LDO, but have a high quiescent current (2uA on Vin and 15uA on Vout n active mode, so 17uA. ). Voltage could be ok, but quiescent current is too high.@PartialDischarge I have take a look before to the Bq25570. A nice IC. But according to thedatasheet, if Vin drop below 3.3V, Vin is bypassed to Vout. There is no boost converter to Vout. Only to the charger section. So this part is not consistent for my design.I am continuing my searches. I will look too boost converters and not buck/boost. I can limit my Vinmax to 3.3V pretty easily without too many losses. It could be a solution.If you have other idea, I take it

author: Marco
author_rank: Super Contributor
timestamp: May 15, 2022, 08:18:54 am
content: Quote from: JL34 on May 15, 2022, 08:03:48 amTPS610981DSE will output 3.3V in low power mode at far lower quiescent current, LDO is turned off, only problem is that it's boost instead of buck-boost.How about this :https://www.digikey.nl/en/products/detail/ricoh-electronic-devices-co-ltd/RP604K331A-TR/10244715

author: JL34
author_rank: Contributor
timestamp: May 15, 2022, 08:34:16 am
content: @Marco TPS610981DSE is not in stock nowhere. Only TPS61098DSE is, but his Vout is 3.1V like I said.But the Nisshinbo's IC you linked seems interesting. I will study his datasheet.Thanks.

author: PartialDischarge
author_rank: Super Contributor
timestamp: May 15, 2022, 08:38:55 am
content: Quote from: JL34 on May 15, 2022, 08:03:48 amYou have not read the ds correctly. Read it again.

author: tszaboo
author_rank: Super Contributor
timestamp: May 15, 2022, 09:09:26 am
content: I'm just waiting for the comments, that will tell you that: "Why don't you learn a bit of analog, and build this from discrete parts. Back in my day, we built everything from a 2N2222 diodes and 1K resistors. This is your over reliance on integrated circuits, and I'm so much better than you!"

author: JL34
author_rank: Contributor
timestamp: May 15, 2022, 09:10:56 am
content: Quote from: PartialDischarge on May 15, 2022, 08:38:55 amAre you sure? Section 7.3.7 "Buck converter" explain what I said.Maybe I misunderstand?Edit :@tszaboo Yes, it seems to be a good opportunity to learn a bit of analog. I will take a look at this too.Thanks

author: PartialDischarge
author_rank: Super Contributor
timestamp: May 15, 2022, 09:28:47 am
content: Quote from: JL34 on May 15, 2022, 09:10:56 amI understand this is a long and complex datasheet. This device 1) serves your purpose and 2) is available. Read the ds slowly, and buy a board off ebay to play with it

author: JL34
author_rank: Contributor
timestamp: May 15, 2022, 06:12:53 pm
content: Quote from: PartialDischarge on May 15, 2022, 09:28:47 amI have read the datasheet again, and I am pretty sure I am right. As a hobbyist and beginner, maybe I am wrong but :Ondatasheet:In section 7.1 "Overview", page 13, end of page :"In addition to the boost charging front end, the bq25570 provides the system with an externally programmableregulated supplyvia the buck converter."In section 7.3.7 "Step Down (Buck) Converter", page 20 :"The buck regulator input power is internally connected to VSTOR and steps the VSTOR voltage down to a lowerregulated voltage at the OUT pin."As VSTOR is the main output of the energy harvesting input and not battery, if battery is under 3.3V, it is not possible to generate 3.3V.I precise here that my battery will not reach 3.3V.On e2e.ti.com, on post "BQ25570: is it possible to get 3.3v output from BQ25570 Vout? even battery voltage is Less than 3v?" :"The BQ25570 VOUT output is from a buck converter and would require a slightly higher voltage than 3.3V to provide 3.3V output. Can I recommend BQ25505 followed by BQ63024 integrated solution or TPS61170 configured as a SEPIC converter (d/s figure 19 page 21)?"A buck/boost (or here SEPIC) is needed to generate 3.3V with a battery voltage lower than 3.3V. The BQ25570 seem to be a buck boost charger, with a buck converter on top of the battery as output power supply.Moreover, BQ25570 is not available in little quantity (as a hobbyist, I need under 10 pieces for now). The only stock I found is in Rochester Electronics website, but MOQ is 49pcs

author: tszaboo
author_rank: Super Contributor
timestamp: May 16, 2022, 09:37:17 am
content: Quote from: JL34 on May 15, 2022, 09:10:56 amnah, I wasn't criticizing you. I'm fairly sure it is impossible to make these things from discrete parts, and expect the same high performance.I am criticizing other forum users who think that everything can be built from discrete parts. And expect it to work over a wide temperature range, and have the power budget of 1uA.

author: JL34
author_rank: Contributor
timestamp: May 18, 2022, 08:33:31 pm
content: @tszaboo No problem. It was interesting to search about how to design a buck boost converter. I have learn some things. But as you said, it seems difficult to build one with very little quiescent current.After some search, I have found a buck boost IC controller in stock at Mouser EU, at correct price (~2,40€/pcs for 10+pcs), with nice specs. 1,3uA quiescent current, easy to implement, interesting features, and I2C interface : Renesas ISL9122A,datasheet.But I finally would not need a buck boost converter to my design. As the MCU (EFR32BG22) on my board could work with Vin between 1.71V and 3.8V, I think I will just connect my supercap to Vin through a little diode, and do not go above 3.8V to charge the supercap. It should do the job. And if this is not the case, I will use the ISL9122A.Thanks to the participants.