Regulating LiPo battery to 3.3V - Page 1
Forum section: electronics / projects

author: gore
author_rank: Regular Contributor
timestamp: December 28, 2022, 06:08:10 pm
content: Hello,I'm building a portable device which runs on a 3.7V 1500mAh LiPo battery. I'm trying to make it as efficient as possible to prolong battery life, of course. Previously I used a LT1308 to boost it to 5V and then a MCP1603 to take it down to 3.3V. Thing is I don't even need 5V. Only do it to keep it stable as battery charge drops.Is there a better solution in a single package, perhaps? Or a chip which can step it down from 4.2V directly to 3.3V, but I assume I'd run into stability issues even with a low dropout regulator (200mV, for example). The device draws about 100mA @ 3.7V constant. Any device supporting about 500mA would be nice to handle short spikes when transmitting.I can look for parts on TME, Farnell, but I'm trying to figure out the correct way to do it first. Any advice I'd appreciate.

author: Peabody
author_rank: Super Contributor
timestamp: December 28, 2022, 06:40:45 pm
content: I think a very low dropout linear regulator would work fine. By the time your battery gets to the 3.5V dropout level, it will be almost fully discharged anyway. But even then, most of these regulators will just follow the voltage on down. You lose regulation, but that shouldn't matter much with a battery supply.One option might be to go with a 3.0V regulator instead of 3.3V if your devices can handle that. They will use less current at 3V than they do at 3.3V even at the same processor speed.I really don't know what's available in the way of buck converters that would convert directly from 3.7V to 3.3V. I think they need more headroom than that. But others may know of options along those lines.Are you able to put your processor to sleep? That's often the biggest contributor to extending battery life, and that's where linear regulators really shine.

author: gore
author_rank: Regular Contributor
timestamp: December 28, 2022, 06:54:57 pm
content: Quote from: Peabody on December 28, 2022, 06:40:45 pmUnfortunately It needs to run all the time. Processing data, driving LCD user interface etc. I've already disabled most the peripherals I can afford to lose. Radio circuit gets shut off as well when not in use, which reduces power consumption considerably.

author: Miti
author_rank: Super Contributor
timestamp: December 28, 2022, 08:53:23 pm
content: I use MCP1703 in one of my projects, but it only draws few uA in sleep and few mA active. Take a look.

author: thm_w
author_rank: Super Contributor
timestamp: December 28, 2022, 10:58:29 pm
content: What is the actual device in question. As mentioned, will it run on 3V?This question gets asked oftenhttps://www.eevblog.com/forum/beginners/from-6v-to-3-3v-what_s-more-efficient-switching-or-ldo/https://www.eevblog.com/forum/beginners/help-selecting-switching-power-regulator/https://www.eevblog.com/forum/projects/single-cell-lipoly-to-3-3v-regulator/https://www.eevblog.com/forum/microcontrollers/power-c-with-18650/

author: Peabody
author_rank: Super Contributor
timestamp: December 28, 2022, 10:59:04 pm
content: I think pinning down your maximum current requirement may be important in selecting an LDO. It appears that the dropout voltage typically rises as the maximum current goes up. But it might be possible to use two or three ganged MCP1700s to provide enough current for everything while maintaining the 178mV dropout voltage. Or maybe use a second regulator just for the radio.

author: Karel
author_rank: Super Contributor
timestamp: December 29, 2022, 12:13:05 am
content: Here you go:https://www.ti.com/product/TPS63051Real buck or boost with seamless transition between buck and boost mode2.5 V to 5.5 V Input voltage range0.5-A Continuous output current: V IN ≥ 2.5 V, VOUT = 3.3 VAdjustable and fixed output voltage versionEfficiency > 90% in boost mode and > 95% in buck modeThis way you can discharge the battery completely (which means down to 3V).

author: AndyBeez
author_rank: Frequent Contributor
timestamp: December 29, 2022, 12:20:47 am
content: Don't forget LiFePO4 batteries which run at a nominal 3.2 volts in a working range of 3.0V to 3.3VYou could beefficientby removing the buck/boost circuit altogether - unless your system is 3.300 volts dependent.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 29, 2022, 12:43:06 am
content: Check your design, and chances are it can run at 3V or even slightly lower. Regulate to that. Done.3.3V is not written in stone. Many if not most digital ICs these days have a largish operating range.Think outside the box. So to speak.

author: gore
author_rank: Regular Contributor
timestamp: December 29, 2022, 10:37:51 am
content: Great suggestions so far. I'll see how stable the system is on 3.0V and take it from there. If it works, a single 3.0V LDO it is then.

author: Peabody
author_rank: Super Contributor
timestamp: December 29, 2022, 03:52:41 pm
content: Quote from: Karel on December 29, 2022, 12:13:05 amIs there anything like this in a package that would be useable with a breadboard? Is there a VQFN-to-SIP adapter board?

author: Karel
author_rank: Super Contributor
timestamp: December 29, 2022, 04:05:52 pm
content: Quote from: Peabody on December 29, 2022, 03:52:41 pmI don't believe that's a practical option because the layout for that chip is critical.For a breadboard it's better to use an LDO.

author: bidrohini
author_rank: Regular Contributor
timestamp: December 31, 2022, 03:56:02 pm
content: You can consider using this:https://www.mouser.com/datasheet/2/609/ADP7105-1503448.pdf

author: iMo
author_rank: Super Contributor
timestamp: December 31, 2022, 04:26:45 pm
content: I used to use the MAX1724 (5pin sot23, 2caps, 1 inductor), it works from 0.6-0.7V input up, with fixed output for 3.0/3.3/5.0V ..

author: Siwastaja
author_rank: Super Contributor
timestamp: December 31, 2022, 04:27:31 pm
content: Do you really need voltage regulation?If possible, use devices which can be supplied by up to 4.2V.If not possible, e.g. most 3V3 microcontrollers with 3.6V recommended maximum, choose components which can run at tad below 3.3V (like 2.8V; most 3V3 parts can), then pick a very low dropout linear regulator (preferably: one where saturated/bypass operation is well defined, but most are fine anyway), and just let the output voltage drop, losing voltage regulation during the last 20-30% of charge or so.

author: gore
author_rank: Regular Contributor
timestamp: January 01, 2023, 12:18:14 am
content: I can't take the direct battery supply route. Most devices on board are somewhere between 2.7 - 3.6V. So far I've tested the entire system on 3.0V and it's been running without issues for a couple of days. Going from 3.3 to 3.0V saves me a decent amount of energy as well (reading about 16% less power draw). Some of that has to do with a slight drop in LCD backlight. Screen is plenty bright though, so not a problem.So far I've picked out a few very low drop LDO's and some devices suggested in the thread. They are good for 200mV or even less, which allows me to use up most of the charge with a stable output. Battery's getting cut @ 3.3V.Example candidate:https://www.tme.eu/Document/1985cfc4e26f4f29df9db32d8f1b1818/MCP1825-3002EAT.pdf

author: Peabody
author_rank: Super Contributor
timestamp: January 01, 2023, 04:48:37 am
content: It looks like that should work very well. So is there no buck regulator solution in a usable package?

author: mariush
author_rank: Super Contributor
timestamp: January 01, 2023, 06:56:34 am
content: If you want long battery life, a step-down/buck regulator can be more efficient than a linear regulator.But few breadboard friendly regulators will actually be better than ldos, because regulators that run at high frequencies don't like long pins and the breadboard contacts. But you could make a tiny pcb at jlcpcb or somewhere and put the regulator chip and the components it needs on that pcb.For example a chip that looks like it would do this 3.7..4.2v to 3..3.3v is this one, AP61100 :https://www.digikey.com/en/products/detail/diodes-incorporated/AP61100Z6-7/11696569It's easy to use, it only requires a small inductor, a couple ceramic capacitors and a couple resistors to set the output voltage, but the components have to be quite close to the chip.The chip can reach 90% efficiency which is better than a ldo (ex 3.7v in, 3v out = 81% efficiency) and the quiescent current (idle power consumption) is very low at 15uAHere's a second example ... a slightly less efficient chip but easier package to solder by hand:https://www.digikey.com/en/products/detail/diodes-incorporated/AP3418KTR-G1/4470871

author: Peabody
author_rank: Super Contributor
timestamp: January 01, 2023, 07:23:52 pm
content: I was hoping a module maker would deal with the layout issues. But I don't see any buck converter modules that convert LIPO voltage to 3.3V. I would have thought that if the switching oscillator could go to a 100% duty cycle, headroom wouldn't be an issue. But apparently that's not the case.Incidentally, what specs in the datasheets of those two Diodes Inc. buck converters you linked to would tell me what their dropout voltage or minimum headroom is?

author: Siwastaja
author_rank: Super Contributor
timestamp: January 01, 2023, 07:33:23 pm
content: Quote from: Peabody on January 01, 2023, 07:23:52 pmThere are switcher ICs that can go to 100% duty operation, but it rules out any that uses N-channel switch with bootstrap gate drive supply. P-MOSFET based switchers usually can go to 100%. Maximum duty is mentioned in the datasheet.If you pick simple, highly integrated (low pin count) parts, layout is not that difficult if you just follow the example strictly.

author: Peabody
author_rank: Super Contributor
timestamp: January 01, 2023, 08:04:38 pm
content: I think this is what I was looking for:https://www.adafruit.com/product/2745It says it will output 3.3V with input voltage as low as 3.5V. But I see nothing like this on Aliexpress or Ebay. Perhaps I'm not searching for the right thing. Or perhaps it's just not enough better than an LDO to be worthwhile, or not better at all for projects that sleep most of the time.

author: mariush
author_rank: Super Contributor
timestamp: January 01, 2023, 08:20:08 pm
content: For the AP61100, you can look in the datasheet:https://www.diodes.com/assets/Datasheets/AP61100-AP61102.pdfIt should work fine at close to 100% duty cycle though.For example, see page 14 where it explains how you can determine the Ton period which like Toff must be minimum 70ns :The AP61100/AP61102 device is a 2.3V-to-5.5V input, 1A output, fully integrated synchronous buck converter. Refer to the block diagram inFigure 5. The device employs constant on-time control to provide fast transient response and easy loop stabilization. At the beginning of eachcycle, the one-shot pulse turns on the high-side power MOSFET, Q1, for a fixed on-time, tON. This one-shot on-pulse timing is calculated by theconverter’s input voltage and output voltage to maintain a pseudo-fixed frequency over the input voltage range.Ton = Vout / ( Vin x Fsw)whereVIN is the input voltageVOUT is the output voltagefSW is the switching frequencyThe off-time duration is tOFF and starts after the on-time expires. The off-time expires when the feedback voltage decreases below the reference voltage, which then triggers the on-time duration to start again. The minimum off-time is 70ns typical.See Figure 15 on page 8 for switching frequency vs load - in your case at around 0.1A you're looking at around 500 kHz switching frequency.So for example let's say 3.1v in, 3.0v out, 500 khz switching frequency ...Ton = 3 / 3.1 x 500,000 = 1.935e-6 or 1935 nanosecondsPage 19 has example of pcb layout - it's only missing the connection to enable pin, which could be permanently connected to VinAs for the second regulator I suggested, the datasheet says it can do 100% duty cycle, so no worries.

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 01, 2023, 08:26:40 pm
content: In many cases, lowering the operating voltage and using a LDO is the simplest, cheapest and even sometimes more efficient approach (due to the fact that buck or buck/boost converters often have a quiescent current much higher than the low Iq LDOs that are ubiquitous these days.) Just do the maths and decide. No way around it.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 02, 2023, 01:22:54 am
content: I'm wondering why the device needs 100mA continuously to run. You give very little information about your device, but the way to get power consumption down is to analyze each part carefully.For real low power devices the quiescent current of a voltage regulator can be a significant factor, but these days a few handfuls of uA is enough to run an SMPS. The TPS6305x mentioned earlier has apparently a 65uA quiescent current. Microcontrollers can also run on less than 1mA/MHz, so where is that other 99mA going? Radio's and LCD's can be very power hungry. Radio's typically run at a very low duty cycle (less than 0.1% of the time on) If the receiver has to be on, then you could revise your protocol. for example, a mains powered transmitter is always on, and your battery powered device only checks in when needed.With LCD's, the backlight is often a power hungry thing, but there are a bunch of technologies that can suck less power out of your battery. A monochrome reflective LCD is an obvious choice, maybe E-paper is fit for your application. The Sharp Memory LCD's are also crisp and need very little power. If you need your display to emit light, maybe an O-led display is suitable, combined with turning on as few pixels as possible.Software design is also an important factor. Writing "arduino" code and wasting cpu cycles in delay loops is just plain horrible.But to me, trying to extends the battery life of a device that sucks 100mA and then only asking a question about some voltage regulator is very odd at least.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 02, 2023, 01:30:12 am
content: Quote from: gore on January 01, 2023, 12:18:14 amWhat sort of shortsighted attitude is that?Of course it is a problem.If you want to extend battery life, turn down the backlight as far as possible. Every emitted lumen sucks the battery dry.

author: gore
author_rank: Regular Contributor
timestamp: January 02, 2023, 03:19:17 pm
content: Quote from: Doctorandus_P on January 02, 2023, 01:22:54 amIt's a bicycle computer. MCU consumes roughly 20mA. I can probably get it down to about 15mA by further reducing cycles. Radio's about 10mA when receiving. It gets data from two transmitters multiple times per second (one for speed, another for cadence and power), depending how fast both the wheel and the cranks are rotating. There are other devices on board. EEPROM, RTC, barometer, magnetometer, accelerometer, gyroscope, MicroSD card. But those make up just a tiny fraction. The rest gets consumed by LCD.100mA overall comes from the LCD running at 100% duty. That is if you want to see the screen clearly when the Sun's up. It's user selectable, whether you want it blazing, or to dim the screen manually/automatically(LDR) based on ambient light conditions so save power. A monochrome reflective LCD would consume a lot less, but hey, no shiny colors. As for software, I'm trying not to be wasteful. There are no delays. If I make a request, say from the barometer, I go do something else and come back later collect when it's finished. And I'm not measuring atmospheric presure all that often.Values on the LCD are only updated when they change, of course.I may not save all that much from a regulator alone given the whole picture, but the question was just bugging me a little as I was going through all the components.

author: mariush
author_rank: Super Contributor
timestamp: January 02, 2023, 04:05:22 pm
content: Honestly the interface on that display is horrible to me. Don't really like that mess of colors and I especially don't like the different sized numbers but that's up to you. The font is also bad, really need at least 1-2 empty lines between 1 and the other digits - that "141" looks really bad to me in the picture. I'd suggest checking out websites likehttps://www.dafont.com/bitmap.phpfor fonts that have good fonts for lcd displays, to have readable numbers. See the fix width fonts (and then adjust width of some digits to squeeze more numbers horizontally) , or bitmap fonts, lcd fonts etc etcIt may even make more sense to have a horizontal strip that switches between 2-3 pages every 3-5 seconds, for the least important data, instead of displaying 6-9 numbers that change less often. Or have a button that would allow user to "flip" between "pages" easily. You'd probably want at least a button, or maybe 2-3 (up / down , select/enter or esc/back if long press or whatever)I think Transflective would give best brightness without backlight, but there's fewer displays with backlight AND transflective.For example here's a 2.7" 400x240 Sharp display ... says 350uW (no backlight) power consumption :https://www.digikey.com/en/products/detail/sharp-microelectronics/LS027B7DH01A/5054067Could probably make your own backlight with a bunch of right angle surface mount leds.At that size, you could probably add a solar panel above the display and that could be enough to produce 20-50mA and power your product while backlight isn't on.

author: gore
author_rank: Regular Contributor
timestamp: January 02, 2023, 05:38:13 pm
content: The layout can be adjusted by the user in the menu, but adding extra fonts is a good idea. This font it a little cramped up (only one pixel separates 4 and 1). I just prefer to see everything at once in relatively small numbers. The LCD has a touch panel, so there's no need for any buttons.Those screens looks interesting. I'll get one and see how well they work.Added extra pictures with a better angle.