I'm going to use 1S Li-po, 3.7V. ESP8266 needs 3.3V and it takes 350mA peak on startup. When running it needs about 70mA.

The ESP task is to wake up, measure, connect to wifi and post data to server. It will wake up every 2 hours. I'm wondering which regulator is better for low power modules, LDO or switching. I know that LDO efficiency is a lot less efficient but they have lower quiescent current. On the other hand the switching offers better efficiency. Which one I should use?

  • \$\begingroup\$ Well, what requirements do you have for a regulator? \$\endgroup\$
    – PlasmaHH
    Dec 1 '16 at 20:21
  • 3
    \$\begingroup\$ "I know that LDO efficiency is a lot less efficient" - No it isn't. Dropping 3.7V to 3.3V with a linear regulator is 3.3/3.7 = 89% efficient. Decent buck converters are in the same ballpark, cheap crappy ones are probably significantly worse. A good buck converter designed for these exact specs could maybe reach 95%; probably not worth the hassle over a linear regulator imho. I would, however, worry about the minimum voltage drop over the linear regulator; pick yours carefully. edit: I should read more carefully; Li-Po source. Its voltage may be over or under 3.7V, changing things... \$\endgroup\$
    – marcelm
    Dec 1 '16 at 20:25
  • \$\begingroup\$ Continuing this; you probably will need a switcher, not because of efficiency but because the battery voltage range is too diverse for the ESP. See this related question (in fact, this might be a duplicate). \$\endgroup\$
    – marcelm
    Dec 1 '16 at 20:35
  • \$\begingroup\$ @PlasmaHH Li-po battery, so Vin 3.7-4.2V, Vout 3.3V, I'm not sure about Iout, ESP needs some time to boot up and it needs 350mA (maybe I can fit into Ipeak). I'll measure this time tomorrow. As I mentioned earlier 70mA when running. Eficiency as high as possible, quiescent current as low as possible \$\endgroup\$
    – KRol
    Dec 1 '16 at 20:38
  • \$\begingroup\$ @marcelm I think the ESP8266 can itself tolerate from \$3.0\:\textrm{V}\$ to \$3.6\:\textrm{V}\$. The Li-Po starts out almost \$4.2\:\textrm{V}\$ with low load and is nearly empty by about \$3.4\:\textrm{V}\$. It may still be possible to consider a linear (some guarantee a max of \$300\:\textrm{mV}\$ overhead) for operating the ESP8266, running it at the bottom of its range, \$3.0\:\textrm{V}\$, using for example the LT1763 (which will support \$350\:\textrm{mA}\$.) \$\endgroup\$
    – jonk
    Dec 1 '16 at 20:41

Good discussion already. I'll summarize the linear option as an answer.

  • A datasheet for the ESP8266 says that it can tolerate from \$3.0\:\textrm{V}\$ to \$3.6\:\textrm{V}\$.
  • A 1S Li-Po starts out almost \$4.2\:\textrm{V}\$ with low load and is nearly empty by about \$3.4\:\textrm{V}\$.

That leaves only about \$100\:\textrm{mV}\$ of headroom towards the end of battery life and that's probably not enough. It's almost certain that you'll need at least twice that much, using an LDO at \$70\:\textrm{mA}\$ and perhaps three times it at the initial \$350\:\textrm{mA}\$ you mentioned.

But it still may be possible to consider using a linear regulator, if you choose to operate at a lower voltage. One that is at or below \$3.1\:\textrm{V}\$. Sure. That's not much wiggle room. But at least it's non-zero. Still, you may also have to consider what else surrounds the ESP8266, too. And you've asserted the need for \$3.3\:\textrm{V}\$ but you haven't disclosed whether or not perhaps \$3.0\:\textrm{V}\$ or \$3.1\:\textrm{V}\$ could be successful. (Okay. I don't know of a fixed \$3.1\:\textrm{V}\$ linear LDO with low quiescent current. So probably \$3.0\:\textrm{V}\$.)

Given all of the above, all I can suggest regarding a linear LDO option is something like the LT1763. It may meet your needs. It's quiescent current is about \$30\:\mu\textrm{A}\$, too, and requires at most \$300\:\textrm{mV}\$ of overhead for your case. So perhaps.

Given a short search (you really should do your own), I did find this from TI: TPS783xx. The spec is below your peak startup current, but well above your operating current. And the quiescent current is extremely low, I believe.

  • \$\begingroup\$ I'm searching though mouser for LDO with lower quiescent current. Do you know any? \$\endgroup\$
    – KRol
    Dec 1 '16 at 21:10
  • \$\begingroup\$ @KRol No, not offhand. That's usually considered "low" and, in fact, it's called out right at the top of the datasheet as an ad. And in the text they call forth "Quiescent current is well controlled; it does not rise in dropout as it does with many other regulators." It is, however, very temperature dependent (so they haven't attempted a Wyatt topology, I suppose.) At the active currents you are talking about, I don't normally expect better. But here's one: ti.com/lit/ds/symlink/tps783.pdf \$\endgroup\$
    – jonk
    Dec 1 '16 at 21:42

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