Voltage regulator for primary battery

[jmarcelino]

The LM3281 solution based on the reference design is pretty good for most purposes?

[Eric24]

@danielm as an alternative to the LM3281, you might consider the TPS63025x. It's more expensive, but I personally like it because it's slightly more efficient and includes boost mode that may get a little more power out of a dying battery, as well as allowing you more choices of primary cell chemistry.

But note that a single LiSoCl2 cell can typically not provide the peak current needed during radio transmission. Depending on the radio(s) and transmission duty cycle needed by your application, this can generally be solved by adding a small "super cap" in parallel with your battery. There are also hybrid batteries available (from Tadiran and ohters) that include the super cap inside the battery, but I don't see much need for those unless you have physical constraints that prevent you from adding your own cap externally.

[robert-hh]

@danielm The Pololu module I mentioned is using the TPS63060 chip, similar to the TPS63025 device, but with a slightly wider input voltage range. So now you have the choice.

[jmarcelino]

If you want buck/boost in a single drop-and-forget package that is more "production-ready" (SMT) than the Pololu module then the Murata LXDC2SCAAB is pretty good.

I actually planned to use this first for my L01 board but the project "pivoted" to a different power source which is not compatible with the input range.

[jmarcelino]

For battery maybe check this one, it should deliver the peak current needed even without supercap:

http://www.tadiranbat.com/assets/tl-5920.pdf (or 5920/B with a molex connector termination )

[robert-hh]

@jmarcelino Looking at that datasheet and thos of other vendors it looks as if these kind of batteries and not suitbale anyhow. The ESP32 based Pyboards need 80..120 mA average current when runnig. At that consuption, according to the linked data sheet the battery voltage goes down to 2.8 V and the capacity is reduced to 2 Ah. A single 18650 LiPo accumulator performs much better.
I made this reasoning a while ago too for an set-up required to run on battery, and after seeing the data of primary batteries, I moved to a rechargeable battery. In this case simple lead battery, since size & weight did not matter, but the temperature range should go down to -20°C at least.

[jmarcelino]

@robert-hh
I think these batteries have a place in applications where most time is spent in deep sleep and most of the runtime will be with WiFi off (avg consumption around 30-40mA) and occasionally send some data.

Particularly they're a good fit if you can have WiFi off other than for very short periods and use for example LoRa or Sigfox to send data.

If you want WiFi up and running a lot of the time then probably no.

Lead acid, LiPos, etc all have their own set of constraints and issues so I don't see there being a single best solution for this. Definitely good to evaluate all the options - and excellent to discuss them here in forum :-)

[danielm]

Thank you all for you replies, it is a very interesting discussion to read and learn from.

We will use regulator from TPS630xx product range.

Current use-case for battery powered devices is to deep sleep for most of the time and send updates (approx. 30 bytes) via raw LoRa. WiFi will be enabled only during configuration and troubleshooting. In these cases we will use external power source if the battery cannot supply required current.

[Eric24]

@robert-hh I'm just curious what kind of "total life" you're seeing with the LiPo. It's been my experience that "very long life" products (i.e. 3+ years on a battery) can't use LiPo's because of their higher self-discharge rate (i.e. this just won't last that long, regardless of how little current the powered device needs). That may not be a factor in your application, but if you've found a LiPo with the ability to last 3+ years without recharging, I'd love to learn about it.

[robert-hh]

@Eric24 As always, it's a balance between power consumtion and storage time. Chargeable batteries can source a high current, but have a higher discharge rate. For LiPo batteries it varies a lot between individual items, and is never in the range of years. If your total energy over three years fits into the capacity of the primary battery, and also the peak current is matched, than for long term operation the battery looks better.

[danielm]

I would like to revive this topic after several months.

Would it make sense to use low Iq LDO instead of switching regulator? If primary battery voltage is 3.6V and regulated voltage should be 3.3V I think it would not be significantly less efficient in comparison to switching regulator.

[jmarcelino]

@danielm
Personally I don't know of a LDO which can regulate up to 0.8A with only 300mV dropout voltage and also have <10 μA quiescent current during deep sleep (unless you control the LDO enable pin)

Also be aware of voltage characteristics of primary cells under these loads, you may not get 3.6V

[danielm]

@jmarcelino
Yesterday I found this one: https://www.mouser.com/ds/2/760/XC6220-837466.pdf

• Dropout voltage approx. 240mA@0.8A
• 8μA (TYP.) in PS mode, 50μA (TYP.) in HS mode

Anyway primary LiSOCl2 battery is hardly able to deliver more that 200mA without internal supercap. I am thinking - what if smaller LDO (e.g. 250mA) was used with large capacitor or supercapacitor on the output to handle power spikes of LPWAN radios and/or WiFi?

[robert-hh]

@danielm I do not know which battery you are looking for. But even for a D-sized battery the output voltage will drop to 3.1V at 200 mA.
A supercap can support that. To tell the total energy to be stored you have to integrate the current over time. I have seen in this board some pictures showing that. That may be sufficient to give an estimate.

[Charly86]

Guys,

May be I missed something, but I'll need 10 Lopy4 for a customer POC. Powered by 3.6V Li-SOCL2 battery.
What's the problem removing regulator and power all the board with 3.6V? I'm doing this for a lot of devices without any problem. Is there something on Lopy4 that does not support 3.6V?
Thanks

[robert-hh]

@charly86 What's the problem with the regulator? It works well, and if the input voltage gets too low, it switches to bypass mode.

[Charly86]

@robert-hh Yeah I saw that, thanks, was just asking why we need if power source is 3.6V, in my case if not needed I'll remove it, each uA won in my case is good to take.

[miroslav.petrov]

I know this is an old topic but someone can find the information useful.

A perfect buck/boost converter for Li-SOCl2 batteries with fuel gauge is LTC3335. It can limit the input current from the battery in order to preserve its capacity because Li-SOCl2 batteries’ capacity drops when high currents are drawn from them. A good suggestion is to add a supercapacitor to cover the high current requirements while transmitting over the radio.

[livius]

@miroslav-petrov said in Voltage regulator for primary battery:

LTC3335

But it is quite expensive or maybe i am looking wrongly...