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ESP8266 unstable when using ceramic cap, but stable with electrolytic
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synoptica:
Hi brains trust!

I'm working on an ultra-low power ESP8266-based sensor network for my home.   I'm trying to keep them as simple as possible, and run them off either a single 18650 cell, or 3x AAA/AA cells (got a ton lying around!)

I'm using an HT7333 regulator for their low dropout and quiescent current (datasheet: http://www.angeladvance.com/HT73xx.pdf)

With no caps, this regulator cannot provide stable power to the ESP - it regularly crashes.  If I throw a 22uF electrolytic across GND/VOUT, it's rock solid, but will drain the batteries over the course of a couple of weeks.  I grabbed a reel of 22uF multilayer ceramic SMD caps, but I'm getting similar instability to when no cap is used.  I specifically chose the ceramics for their low-leakage properties.

What am I failing to consider here?  I realise that the ceramics are non-polarised - would such an application require polarised caps?

Thanks in advance!
wraper:
Many LDOs are unstable with ceramic capacitors due to their low ESR. Many datasheets don't mention this. If you see electrolytic/tantalum output cap in example in datasheet, you should assume LDO is not suited to work with MLCC. Those which are stable with MLCC usually say it explicitly in datasheet or at least provide suitable ESR range.
http://www.ti.com/lit/an/slva115/slva115.pdf
wraper:

--- Quote ---If I throw a 22uF electrolytic across GND/VOUT, it's rock solid, but will drain the batteries over the course of a couple of weeks.
--- End quote ---
It has nothing to do with capacitor. 4uA quiescent current of HT73xx is higher than leakage current of non faulty electrolytic capacitor. ESP8266 is dominating in current consumption unless it's in Power OFF mode.

synoptica:

--- Quote from: wraper on January 02, 2019, 11:55:07 pm ---
--- Quote ---If I throw a 22uF electrolytic across GND/VOUT, it's rock solid, but will drain the batteries over the course of a couple of weeks.
--- End quote ---
It has nothing to do with capacitor. 4uA quiescent current of HT73xx is higher than leakage current of non faulty electrolytic capacitor. ESP8266 is dominating in current consumption unless it's in Power OFF mode.



--- End quote ---

That's interesting...  It's definitely going into deep-sleep correctly, but you're right - thinking back now, when I was only getting about a week or so, I was still using an AMS1117.

That being said, I though I read that an electrolytic would drain somwhere in the low-milliamps range. Maybe it's time to shell for a uCurrent Gold ;)

Thanks for the advice on the MLCC caps though - it's good to know!

What would be your recommendation in this instance - a low-leakage electrolytic, or tantalum?
wraper:
Small electrolytic caps usually draw nanoamps after they stay some time under voltage. Just open electrolytic cap datasheet, it's usually specified 3-4 uA maximum at rated voltage (and will drop at lower voltage). AMS1117 have around 5mA quiescent current.
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