MicroPython Forum (Archive)

I just got a S2 Mini board, and I'm trying to power it from a single 18650 Li-ion cell. The 18650 is the input of a HT7333 LDO regulator which nominally outputs 3.3 V. My battery input is ~3.89 V, my output is ~3.25 V, but something does not work as intended (the board should be requesting a URL and it is not doing so). I added 10 uF capacitors to the input and/or output of the HT7333 but no luck.

The board works from time to time, for no obvious reason. I suspect this is a power issue, as the same board works flawlessly when powered from USB.

What would be a simple, reliable method to power this board from the 18650?

I put 1000uF low-ESR caps on my 26V to 5V SMPS outputs, which are capable of 5A peaks . I also use some 1.5A SMPS buck supplies, which seem to work as well.

Max output current 250mA! Have you got a DSO?

I'd check that any internal current limiter in the HT7333 can handle charging up a 1000uF at turn-on. I didn't see anything relevant in the datasheet.

Thanks for the feedback.

For the record, after exploring a number of options I went with the following option: connect the Li-ion battery to the 3V3 pin of the S2 mini through a silicon diode. The S2 should see voltages in the range of 2.9-3.5 V, which is within specs. This solution is very simple to implement, and should be very energy-efficient

mathieu wrote: ↑

Wed Sep 15, 2021 7:44 pm

I just got a S2 Mini board, and I'm trying to power it from a single 18650 Li-ion cell. The 18650 is the input of a HT7333 LDO regulator which nominally outputs 3.3 V. My battery input is ~3.89 V, my output is ~3.25 V, but something does not work as intended (the board should be requesting a URL and it is not doing so). I added 10 uF capacitors to the input and/or output of the HT7333 but no luck.

The board works from time to time, for no obvious reason. I suspect this is a power issue, as the same board works flawlessly when powered from USB.

What would be a simple, reliable method to power this board from the 18650?

Ht7333 is a LDO with large voltage difference, which is not suitable for this occasion
The better LDO I used before is tps74701, but now it has been replaced with tps63000 DCDC

Not only maximum cell voltage needs to be taken into account, I'd also consider the lower limits of the cell. If battery efficient operation isn't needed, one could use a TP4056 based charging / protection board (which would also handle charging the cell, but then you'll need a relay / FET to disconnect the load while charging) and a step-up board that steps the (say) 2.5 to 4.2 V from the cell up to clean 5V.
I do that when I use ESP32 based dev boards (ESP32 DevKit C, Heltec Wireless Stick) in non-critical testing setups or if backed by solar cells.

In general, you'll want a low dropout, wide input range LDO with a very low quiescent current to maximize efficency.
There's also a excellent video on the topic by Andreas Spieß over on Youtube: https://www.youtube.com/watch?v=FrCgQgahzsI

Also if your cell does not have protection included, you should implement it in your design. DW01-P can be used for that. (https://cdn.sparkfun.com/assets/learn_t ... et_V10.pdf)

best regards,
Chris