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I have a need for a voltage regulator such that I can use it to down-convert 5V USB to about 3.3V in order to charge a lithium battery. Ideally:

  • Assuming some users may have a faulty micro USB input voltage, it would be nice if it could support input voltages which range from 4V to 6V.
  • It would be nice if it was not greatly affected by temperature (so for example, if you're charging it outside at -40 degrees, it would be great if the battery could at least hit 3.1V of charge instead of 3.3V). UPDATE: Users have pointed out that below freezing, lithium ion batteries will start to break down because cells will start to plate, so maybe it would be best if the temperature range of the regulator starts between 0 and -20 degrees, or, that the regulator has some thermal protection on it for sub-freezing conditions, or optionally I can leave it up to the user to break his own battery by doing this. If it has an enable signal and my microcontroller comes on at about 2V, then I can warn the user at the very least that what they are doing is destructive.

  • No leakage current. So, for example if it is connected to the battery and the micro-USB is disconnected, it should not consume any current at all.

  • A small package would be very helpful since this is going into a PCB.
  • A feature to be able to shut it down from a microcontroller would be nice (an inverted enable signal would be great bonus, so 0 for on and 1 for off, because the microcontroller and battery could be completely dead).

The battery I am using is FDK America's ML2430-HS1.

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  • \$\begingroup\$ This seems like a pretty comprehensive list. What have you found which is close, but not sufficient? I'm not convinced that "an inverted enable signal would be great bonus,". If there is no power supply, it can not charge that battery, and if there is power then a pull-up or pull-down could be driven. Am I missing something? \$\endgroup\$ – gbulmer Dec 27 '15 at 15:26
  • \$\begingroup\$ @gbulmer I was looking at different regulators on Digikey and Mouser. A lot of them don't show their output leakage currents, so I am not sure what to do. One option is to find a regulator with a slightly higher output voltage and put a diode after it, but the diode will then have a decent voltage drop based on temperature dependence at extreme temperatures. The one thing you're missing is, I'd like the option to cut off the charging from a microcontroller in order to prevent damage to the battery. \$\endgroup\$ – Alexandru Dec 27 '15 at 15:35
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    \$\begingroup\$ @gbulmer Lithium ion batteries cannot absorb overcharge. When fully charged, it is good practice to cut off the charging current. A continuous trickle charge may cause plating of metallic lithium and compromise safety from what I understand. \$\endgroup\$ – Alexandru Dec 27 '15 at 15:37
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    \$\begingroup\$ @Alexandru - "a lot of people" doing a thing doesn't mean it is good. Here is a blurb that you might find interesting "Many battery users are unaware that consumer-grade lithium-ion batteries cannot be charged below 0°C (32°F). Although the pack appears to be charging normally, plating of metallic lithium can occur on the anode during a subfreezing charge. The plating is permanent and cannot be removed with cycling. Batteries with lithium plating are more vulnerable to failure if exposed to vibration or other stressful conditions." \$\endgroup\$ – zeffur Dec 27 '15 at 16:33
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    \$\begingroup\$ @zeffur That is interesting. You can't really stop a rebel user from doing something like this...I guess you'd need an analog, temperature dependent circuit to disable charging once the micro-USB is plugged in under such conditions. There are so many factors to account for, and yet nobody seems to have made a solid battery charging package for us all to use which accounts for all of these use cases?! \$\endgroup\$ – Alexandru Dec 27 '15 at 16:38
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TP4056? This is my go-to battery charger controller. It is a linear design so not really efficient but otherwise it is an all-in-one design.

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  • \$\begingroup\$ This is not a standard part number. I don't even know who the manufacturer is, and the data sheet I was able to find online is not helpful at all. How can you prove it meets all my criteria? Not to sound like a bigot or rude, but I don't think your suggestion is for me. \$\endgroup\$ – Alexandru Dec 27 '15 at 15:46
  • \$\begingroup\$ @Alexandru I use it day to day. It, and its and the smaller-current variant TP4057, is deeply integrated into my kits. I build my own battery packs. TP4056 is almost always the charger control chip in those. \$\endgroup\$ – Maxthon Chan Dec 27 '15 at 17:37
  • \$\begingroup\$ I do believe you, but its not a standard part and I can't seem to find it on Digikey or Mouser, or a proper data sheet, so I can't really affirm it meets my needs, can I? I believe it works for you though, but just because it works for you doesn't mean it will work for me. \$\endgroup\$ – Alexandru Dec 27 '15 at 18:18
  • \$\begingroup\$ @Alexandru Use Google and you will be able to find its datasheet. I know it meets all your requirements as my battery banks are subjected to the same level of stress as you indicate here. \$\endgroup\$ – Maxthon Chan Dec 27 '15 at 18:20
  • \$\begingroup\$ The TP4056 and 7 are generic charger ics from no name Japanese manufacturers. There are a bunch of single IC 5V to Lipo charger ICs of similar types. The Linear LTC4056/7 and Microchip MCP73831/2 are similar. \$\endgroup\$ – Passerby Dec 28 '15 at 10:13
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You've asked a fun question. Because you need two things. (Or just the first thing, it does have a Shut Down pin after all.)

  1. ADP3301ARZ-3.2 - This is a linear Regulator that regulates down to 3.2 with very good temperature compensation.
  2. 2N7002PW - an NMOS that I picked to have a relatively small R-on when it's Vgs = ~5V

Now for a hook up diagram: Please note that I'm not including Caps in the diagram, You will need them, please read the Datasheet.

schematic

simulate this circuit – Schematic created using CircuitLab

Now, when there's no input voltage, the NMOS turns off and the linear reg can't soak up current. To be doubly sure, you can add a PMOS tied similarly, but I've not found that to be necessary ever.

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Have a look at MAX1551 it is usb/ac single cell Li+ charger. It does not have Chip Enable.

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