2 cell ic charger

Hi everyone! I'm searching an easy to use SMD ic to charge a two cell lipo battery pack from a USB. It's a small one, about 700mah, and I don't need high current charge, it only must be cost-effective and with as less accessories components as possible. I write here because I've never designed a lipo charger, even if I use some lipo battery packs.
Thanks!!

Usb supplies 5 v .
Two cell lipo requires 7.4 v minimum so a boost supply is a must.
May be easier to look at a different battery type as lithium chemistry has more complex charging requirments above one cell

Yeah, you're right. I was wondering if it's better to lower the voltage of a 2S with a linear regulator or to use a one cell with a boost up to 5v... Which one would you advise?
Thanks!!

Subsea:
I was wondering if it's better to lower the voltage of a 2S with a linear regulator

How will this help you to charge the battery?

Subsea:
Hi everyone! I'm searching an easy to use SMD ic to charge a two cell lipo battery pack from a USB. It's a small one, about 700mah, and I don't need high current charge, it only must be cost-effective and with as less accessories components as possible. I write here because I've never designed a lipo charger, even if I use some lipo battery packs.
Thanks!!

What about Balancing the two cells?
Do you think you will need that?

Do you have "space" for a DC-to-DC Boost Inverter?
something like this ...
DC-to-DC
or build your own.

Then you can Boost the 5 Volts USB @ 500ma input to 10 Volts @ 250ma output
Then use a simple 2S LiPo Charger IC via the 10 Volts.

Something like this ...
MCP73213 - Non-Balancing 2S LiPo Charge IC with just 3 external components
MCP73213

Hi! The idea was building the DC-DC by my own on the board, but not to boost the 5V, but the 3.6 of a 1S lipo. That's because the DC-DC converts are more efficient than linear regulator (and of course I don't want to waste battery in heat), and the chager for 1S from 5V are very simple. Do you think this can be good? So I won't even have to balance the two cells. Could you advise me a chrger and a DC-DC converter? Today I'll go through DigiKey and the most common IC manufactores to find one :wink:

Thats what i would do for simplicity.

You can run an atemega directly from a 1 s lipo at lower voltage, depends what your perhiferals need.

May have to swap the 16 MHz crystal fo 8 though.

Subsea:
Hi! The idea was building the DC-DC by my own on the board, but not to boost the 5V, but the 3.6 of a 1S lipo. That's because the DC-DC converts are more efficient than linear regulator (and of course I don't want to waste battery in heat), and the chager for 1S from 5V are very simple. Do you think this can be good? So I won't even have to balance the two cells. Could you advise me a chrger and a DC-DC converter? Today I'll go through DigiKey and the most common IC manufactores to find one :wink:

Sorry, I misunderstood because the TITLE says: "2 Cell IC Charger".

The MAX1555 Chip, used in Funduino, is a USB Powered, 1 Cell LiPo charger.
ZERO external components.

I gave you a link for a $4.00 DC-to-DC Boost Inverter in previous message.
Input as low as 3 volts
Output at 5 volts
Might work?

You do not want to discharge your LiPo below a certain voltage.
I've read ...
If LiPo is discharged below 3.4 volts to 3.1 volts then battery is "damaged".

Hi!
Thanks for replying guys!
@mrsmu i meant a Dc-dc convert IC :wink: yes, the maxim was exactly what I said to be "easier", no external components, low price!
@board yes, I know that but is so much easier to run at 5V. I don't know if it runs at 16 mhz with aa 3V power supply, but I don't think so.
Thanks again!!

Subsea:
Hi!
Thanks for replying guys!
@mrsmu i meant a Dc-dc convert IC :wink: yes, the maxim was exactly what I said to be "easier", no external components, low price!
@board yes, I know that but is so much easier to run at 5V. I don't know if it runs at 16 mhz with aa 3V power supply, but I don't think so.
Thanks again!!

Ohhh, a DC-to-DC inverter IC ...
MAX 1682/1683 Voltage Doubler Charge Pump
needs two external capacitors.
5.5 Volts INPUT (max)
11 Volts OUTPUT (max)

This might work ...
USB => MAX1555 => Li-Ion Cell => Max 1682 => Arduino

Wow! Thanks very much!! Let me look at the datasheet :slight_smile: :wink:

Just saw the sheets! Wow, great IC! But if it doubles the voltage that means that I'll have 6.4-8 Vout, and so I'll need to use a linear regulator... I only complain about the efficacy of the linear... I'm thinking I can use a 1 IC only solution, even if I'll have to use an inductor. This evening I'm going to browse to search some ICs, I'll let you updated :wink:

Subsea:
Just saw the sheets! Wow, great IC! But if it doubles the voltage that means that I'll have 6.4-8 Vout, and so I'll need to use a linear regulator... I only complain about the efficacy of the linear... I'm thinking I can use a 1 IC only solution, even if I'll have to use an inductor. This evening I'm going to browse to search some ICs, I'll let you updated :wink:

Maxim makes some cool chips.
Sorry, I thought you were looking for "Power In" ( +6.6v or greater ) for Arduino.
OK, so you need LiPo directly to Regulated 5 Volts?
Hmmm ...

USB => MAX1555 => LiPo => MAX682 => Regulated 5 Volts (250 ma, no Inductor)

USB => MAX1555 => LiPo => LT1935 => Regulated 5 Volts (1 Amp & Inductor)

Enjoy ...

Yes! That would be the target!! 8)
I browsed in Maxim syte and found some really fun ICs! My knowledge was restricetd to the 232 and the MAX6953 I used in a project... The most relying thing is that some ICs has the switching inside the IC! ;D
Tomorrow I'll finish my trip on the net and propose to you what I found.
Thanks!!

Hi! Here I am again! So sorry I couldn't go on with the project during this time. However, I've seen the LT1935, but I also found online so many ICs that have the same specs and lower price, for instance the MAX1896. So the question is: how do I choose a DC-DC converter?
For the battery IC... Wow!! That's really great! Thanks a lot!!

Subsea:
Hi! Here I am again! So sorry I couldn't go on with the project during this time. However, I've seen the LT1935, but I also found online so many ICs that have the same specs and lower price, for instance the MAX1896. So the question is: how do I choose a DC-DC converter?
For the battery IC... Wow!! That's really great! Thanks a lot!!

How many milliamps does your project draw via the +5 volt connection?

Hi! From 600 to 1000! I also saw this one, I think it's the other one that best suits with the lt1935: LTC3426 Datasheet and Product Info | Analog Devices
Maxim makes amazing ICs but don't give more than 400-500 mA in their ICs. I checked many producer sites and I can say the max 1555 is one of the best (less external components needed, good charging current) I did the same search for the regulator, and I saw that the two of LT have the best efficiency @5V 800-1000 mA.
And of course, thanks for answering;)