Lithium Ion/Polymer USB Battery Charger IC - MAX1555

This handy little IC will correctly and safely charge our Lithium Polymer batteries with power from a USB port or from a DC wall adapter. Max current is limited to 300mA using an external wall supply (3.7V to 7V). Requires almost no external components and will automatically select between a DC source and USB source if both are present. Current is automatically reduced to a trickle when charging is complete.

Lithium Ion/Polymer USB Battery Charger IC - MAX1555 Product Help and Resources

Core Skill: Soldering

This skill defines how difficult the soldering is on a particular product. It might be a couple simple solder joints, or require special reflow tools.

3 Soldering

Skill Level: Competent - You will encounter surface mount components and basic SMD soldering techniques are required.
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Core Skill: Electrical Prototyping

If it requires power, you need to know how much, what all the pins do, and how to hook it up. You may need to reference datasheets, schematics, and know the ins and outs of electronics.

3 Electrical Prototyping

Skill Level: Competent - You will be required to reference a datasheet or schematic to know how to use a component. Your knowledge of a datasheet will only require basic features like power requirements, pinouts, or communications type. Also, you may need a power supply that?s greater than 12V or more than 1A worth of current.
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Looking for answers to technical questions?

We welcome your comments and suggestions below. However, if you are looking for solutions to technical questions please see our Technical Assistance page.

  • Member #833048 / about 7 years ago * / 1

    The website is nice, but arabic people can't benefit from site because content is not arabic, so for arabic content about lithium batteries ( )

  • Member #83274 / about 11 years ago / 2

    After looking at the datasheet, it appears that this chip does not turn the charging voltage off after charging is complete. According to the following article:

    "Li-ion cannot absorb overcharge, and when fully charged the charge current must be cut off. A continuous trickle charge would cause plating of metallic lithium, and this could compromise safety. To minimize stress, keep the lithium-ion battery at the 4.20V/cell peak voltage as short a time as possible.

    Once the charge is terminated, the battery voltage begins to drop, and this eases the voltage stress. Over time, the open-circuit voltage will settle to between 3.60 and 3.90V/cell."

    • The chip does indeed turn off the charging voltage off at ~4v or when the charge current drops below 50mA if memory serves me right

  • Member #372201 / about 11 years ago / 2

    So is this in stock since its got the green dot and says there's 2,771 in or are we still to assume it is discontinued with no replacement???

  • Thimplum / about 12 years ago / 2

    Ugggg... Why do these chips have to be so big? I mean, how does Sparkfun expect us to have space for this gigantic thing? :)

  • AndyOlivares / about 14 years ago / 2

    I'm wondering if it is possible to draw some current from the Li-ion battery to power my circuit while this chip is charging it. Is there any problem doing that?

    • Dirk / about 13 years ago / 1

      Yes you can draw current with your circuit while the battery is Charging the max1555 is made for this purpose.
      Just make sure your Circuit takes less current
      than 100mA on USB or 350mA on Adapter, or the battery
      will not charge but drain.
      If you do this its always a good idea to monitor the
      battery voltage level as well.

      • Invntor / about 13 years ago / 1

        In past designs it was not allowed to have a load attached to a LiPo battery under charge because the charger is looking at current draw during the pre-charging and charging phases and voltage during the terminal phase. Having a load attached and drawing current made these measurements difficult and interfered with the charging process. Is this still not true for the MAX1555? Is there a document that describes the 100mA limitation? Thanks!

        • If you take a look at the datasheet it will mention that charging is limited to 100mA if connected to a USB supply, and 280mA when power is applied to the DC pin. I do not know where Dirk got the 350mA limit from.

          Concerning drawing current while charging. I do not know if this is possible, but the typical application does seem to suggest that this is possible, as the schematic notes "To system load" and not "To battery", tho I too seem to remember that there might be some issues with that. With system load they could of course mean the load of the chargin chip, being the battery, however that would be quite silly labeling.

    • NXTreme / about 13 years ago / 1

      You could just power your circuit from the power source that powers the charger. That would be a slightly harder circuit to build but it shouldn't complicate things too much.

  • Doctor_X17 / about 9 years ago / 1

    So, here's a question about this IC: can I use it to charge ANY Li-ion or LiPo battery? For example, I picked up some DEWorld batteries from RadioShack, which have a PCB protection circuit built-in. Can I safely charge such batteries with this IC?

  • Member #425531 / about 10 years ago / 1

    can this charge a lithium-ion coin cell battery like those found in some laptops?

  • Member #306611 / about 10 years ago / 1

    Referencing the datasheet the quoted max USB supply current is 3mA with a max voltage input of 6V. How is it then possible that the output is 4.242V at 100mA (at max charging)? This parameter does not seem to make sense with basic rules of electronics and power and when examining the circuit in the data sheet it seems as though the FET draws the current directly from the voltage source. If I am just reading the data sheet incorrectly please inform me but otherwise if anyone has an answer to this question it would be greatly appreciated.

  • Member #435879 / about 11 years ago / 1

    Just FYI, it's almost impossible to see the product on the quarter. From the SMC ICs page, I honestly thought it was only the quarter. Try adding a very small piece of white paper underneath...

  • Member #83274 / about 11 years ago / 1

    I'm thinking a dime might have been a better choice for scale.

  • Member #332511 / about 11 years ago / 1

    ok so I got it soldered on my board. I am 99.999999999999999999% sure everything is soldered together in the way it needs to and that there are no short circuits. My chip starts making smoke when I plug the battery that will be charged into it. The battery is an 18650 cell. What am I doing wrong?

  • Member #332511 / about 11 years ago / 1

    How are we supposed to attach this tiny tiny thing to our pcb board? I have had no luck. Can anybody help?

    • If you are trying to solder it on solder pads on your PCB board, then I recommend solder paste. You can also use thin solder. If you are just trying to add this to your setup, I recommend taking a look at our SOT23 to DIP Adapter in the related section, because it makes the IC easy to connect to your setup. If you give more specifics to your setup/PCB board you are using, I can give better tips!

  • Are there any chips similar to this that can charge a 2 or 3 cell battery?

  • asselinpaul / about 12 years ago / 1

    You should stock it's big brother, the MAX1811.
    It's good for a lot more mA.

  • Microman / about 12 years ago * / 1

    Could we get a picture of something other than a coin?
    Update: I didn't look close enough to see the tiny ic!

  • Member #234574 / about 13 years ago / 1

    Is it possible to charge two Li-ion button cells in parallel with a single MAX1555?

    • ATtiny Fan / about 12 years ago / 1

      Kinda sorta, if the cells are balanced and have similar internal resistance then maybe, but I wouldn't try it.

  • Member #124120 / about 13 years ago / 1

    I just want to ask: is it possible to charge a Li-ion battery of 7.2V?? Is there any problem doing that??

    • No, these will only charge single-cell LiPo batteries.

      • Electrical Juggernaut / about 12 years ago / 1

        Single-cell battery is an oxymoron. I usually just refer to them as lion secondary cells or just lion cells. Sorry for being a grammar nazi.

  • Pork Rhombus / about 13 years ago / 1

    As far as I can see, the datasheet does not actually mention any trickle charging after the main charge is complete. I'd like to know if this IC does in fact go into a trickle charge mode, and if so, what is the trickle charge current? I want to use it to maintain a back up battery, so external power will almost always be present. I don't want to wreck the lithium cell by continuing to trickle charge it. If you know the answer, please share it ! Thanks.

    • Member #193447 / about 12 years ago / 1

      The device does not trickle charge when the main charge is complete. That is a major error in Sparkfun's description. Li-poly batteries should NEVER be trickle charged. They will be overcharged then and die. If you wish to maintain a full charge it's best to wait for the battery voltage to drop a reasonable amount and recharge. This may be a while as lithium batteries are better than other types in holding a charge with no load attached.
      This charger also does not seem to do a saturation stage when the full voltage is reached. This means this charger will only charge batteries to about 85% of their capacity.

  • EliTheIceMan / about 13 years ago / 1

    I want to use this with the 900mA li-po SparkFun sells. Is it reasonable to assume that from usb(100mA) that it takes approximately 9 hours to charge? I figure the battery will still have some juice but it won't charge at 100mA the whole time either. I'm just looking for an approximate charge time with this chip.

  • Kenta / about 13 years ago / 1

    I'm working on a battery powered setup, but I want to run the uC at 5V, since the sensor I'm using also takes 5V, and the display will probably need the same 5V. Can I safely use this charge IC, which would then connect to the battery, and also connect to a DC-DC step up converter or would there be a feedback loop or anything giving me an unwanted result in the charge circuit?

    • ATtiny Fan / about 12 years ago / 1

      There most likely would as the first post in the comments above shows, the amount of current needed would overload the chip in most cases.

  • Tredlock / about 13 years ago / 1

    When will you have some of these in? I need some soon...

  • AndyOlivares / about 14 years ago / 1

    Is it possible to charge a single cell 3.7V Li-Ion battery (for example with this chip? Any consideration about using this chip?
    Thank you :)

    • Pearce / about 14 years ago / 1

      yes it is possible, we actually use this chip for our LiPoly charger

  • Sam Lanzo / about 14 years ago * / 1


  • Andrew / about 14 years ago / 1

    This chip will be under voltage (2.4-2.7V) when it's unloaded. I really wish I'd known that 45 minutes ago. :P

    • NKT / about 14 years ago / 1

      It has to be to be safe.
      If the voltage floated upwards, you might end up with a very high voltage being shocked into the cell when you connect it, which given how sensitive lithium batteries (and the often built in protection circuits) are might be a nightmare.

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