[REQ] Li-ion battery charger circuit using MCP7383x (Microchip)

[blacknight72]

I need to use Li-ion as a power supply for my PCB. I will use solar power (converted by solar cells) for charging it (or them if I need 2 cells).
But the problem is, I've never design or use a circuit like this before. This is not new, so I think you can help me to do this.
After finding out for a while, I find that I can buy MCP7383x devices of Microchip easily in my country. If you've worked with this device, plz help me.
Thanks.

[pickit2]

Have you got the part number right?
Microchip have loads of helpful data.
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2018&mcparam=en544443

[blacknight72]

Sorry if my question is so silly, but can this circuit charge for Li-ion batteries that used in cell phones (which I will use in my project) ?

[Ichan]

Yes. The cellphone battery mostly is a single cell litium-ion battery with electronic protection circuit inside, it protects the battery from abuse eq. over/undervoltage, overcharge/discharge, overtemperature, etc. Beware that some cheap far-east battery has a "fake" protection circuit inside, charging this kind of battery can lead to a serious problem.

If you will charge the battery while the battery is in use then another thing is needed (at least a P-Channel Mosfet), there is an an application note on microchip website which explain about this, i don't remeber the number but you can try to search for "load sharing".

Be very careful with Li-Ion battery, never use it without a protection circuit!

-ichan

The Application Note:
AN1149: Designing A Li-Ion Battery Charger and Load Sharing System With Microchip’s Stand-Alone Li-Ion Battery Charge Management Controller.

[blacknight72]

I've got a problem when I design circuit for this project. It's about voltage range of devices.
I will use SIM300D and PIC for acquiring data and sending them to the internet over GSM network. A Li-Po (or Li-Ion) battery (3.7V) is the main power source.
SIM300D can operate normally in 3.4V-4.5V but PIC is in 2.3-3.6V.
So I can use battery for SIM300D but not for PIC.
Because all of these things use power from solar power so I have to reduce all power cost to minimum. Do you guys have any idea about regulator for PIC in this case?

In the other hand, solar panels that I can buy from my location is 12V. So that I have to use LM2576-ADJ to ouput 6-7V (charging voltage for MCP73683).

Generally, my idea is:

Solar power (12V) -> LM2576 (7V) -> MCP73683 (charger) -> Li-Po battery (3,7V) -> SIM300D + ( regulator) -> PIC (2.3-3.6V)

Is this the best design for reducing power cost? Any suggestions about this?

[Ichan]

That is a solution, just make sure the regulator (3V3 ?) is low drop-out type, and check if your modem has 3V3 I/O tolerant on both direction.

But for cost reason, i will replace the microcontroller with the one which will work on the li-ion voltage range and also trying harder to find 6V solar panel. These will considerably reduce the cost and better power efficiency as the two regulators will dissipate some power.

Other thing, GSM modem mostly need high current burst (can be 3 - 4 A peak) for a while when it searching for network, consider this on your design.

-ichan

Edit: Don't know about SIM300 but Wavecom modem i have used has Li-ion charging function.

[blacknight72]

My project's target is design a mini station acquiring rainfall, temperature & humidity data and send them to the internet using GPRS.
Because I'm familiar with PIC microcontrollers and I intend to port Free RTOS on the microcontroller, I think PIC32MX family is the most suitable selection. But its operating voltage do not fit to use with battery. What's a pity!

That is a solution, just make sure the regulator (3V3 ?) is low drop-out type, and check if your modem has 3V3 I/O tolerant on both direction.

Microcontroller & SIM300D only have connections in Serial pins (RS232) and we can connect them directly (I've tested it for months and it is okay)

But for cost reason, i will replace the microcontroller with the one which will work on the li-ion voltage range and also trying harder to find 6V solar panel. These will considerably reduce the cost and better power efficiency as the two regulators will dissipate some power.

Actually, there are 6V solar panels but is power is low (1-2.5W) and I'm afraid that it is not enough for this application.
As you know when GSM modem searching for network, sending data through GPRS, it will need high current burst (with SIM300D, it is 2A peak) so I think it will cost much power for this. Besides, I have to send data about each 30s-1min. Time for sleep is not much, then

Other thing, GSM modem mostly need high current burst (can be 3 - 4 A peak) for a while when it searching for network, consider this on your design.

Because SIM300D using battery as its main power source, so 2A current is not a problem with battery, isn't it?

Don't know about SIM300 but Wavecom modem i have used has Li-ion charging function.

Actually SIM300D does have Li-Ion charging function, but I don't know that it is good or not. So I think it will be better when I use a specific device for charging (in this case, MCP7383 of Microchip). Besides, MCP7383 also can charge for Li-Po batteries, SIM300D do not have this function. I intend to use cell phone's battery, so I don't know that charging function of SIM300D will work well with it.
Can you tell me what kind of battery you've used?

Thanks in advance!

[Ichan]

I have to send data about each 30s-1min.

That's many, let's say 10 seconds transmit at 2A every 1 minute, quick calculation that it will need 20 Ampere-Seconds per minute = 1200A-Sec/Hour = 333mAH/H, if you use 1000mAH battery then it will empty in 3 hours. Solar panel can only effective for 6 hour per day (depends on location) so the battery must handle the other 18 hour which mean a capacity of 18 x 0.333 = 6AH, make a safety factor of 2 then you need 12AH battery... ups i might be wrong.

I mostly use "bare" Li-Ion battery with self build protection circuit, i usually use MAX1758 for charging and S8254A (Seiko Instruments) for battery protection. Nowadays cell phone battery with high capacity is available but i think still below 2000mAH. Li-ion battery can supply high current surge, but the protection circuit will limit the current, i think it is mostly around 2C (2 x capacity, 2A current limit for 1000mAH battery). You can test your cellphone battery, if it have a working protection circuit then it will "shut-down" the battery if the current go over the limit.

Using simple load sharing like on the app note above, when the supply is available the battery is disconnected from the equipment which mean on your case if the sun is shining the solar panel must supply the equipment and charging the battery at the same time - then high power solar panel required.

-ichan

[Top]

let's say 10 seconds transmit at 2A every 1 minute

Hey, that's a lot of data... Wouldn't 100mS every minute be more realistic? 2A x 0.1S / 60 = ~3mA average plus say 10mA to keep the radio registered and the micro running = 13mA. Your 1000mAH battery might last for 3 days!

[Ichan]

Wouldn't 100mS every minute be more realistic?

May i negotiate for 1s per-minute? 

Keeping the GPRS connected is costly (depend on the provider), while opening GPRS connection took some time and may need several trial.

...and send them to the internet using GPRS.

Blacknight, how will you send the data? Via HTTP/FTP/e-mail or anything else? I am looking for similar thing for my next project.

Top, do you know how to send an e-mail to Gmail or Yahoo account via GPRS?

-ichan

[blacknight72]

Blacknight, how will you send the data? Via HTTP/FTP/e-mail or anything else? I am looking for similar thing for my next project.

I use SIM300D's TCP/IP Stack for sending data to a web server (using GET method). My server-side script is PHP & MySQL for database server.
We also can send data via a specific port. This will provide us a method for sending binary data with fast interval (only request for opening connection 1 time). But we have to code a service running on server computer to listen data on this port. It will cost much, both money & time.


I want to design a stand-alone station for acquiring data. So I think I have to reconsider about the interval of sending data. Maybe it should be reduced to 2-5 mins. That will make sure that my station can work for 2-3 days without any solar power. (Plz remember that I have 1 microcontroller in and 1 temperature & humidity sensor in my board)

Do you guy have any idea about designing power suppy for GPRS modem & microcontroller with Li-Ion (Li-Po) battery and solar power? I need this mini station can work days by days (except bad weather for days).

Using simple load sharing like on the app note above, when the supply is available the battery is disconnected from the equipment which mean on your case if the sun is shining the solar panel must supply the equipment and charging the battery at the same time - then high power solar panel required.

And I haven't had any idea to solve this yet

[Top]

Keeping the GPRS connected is costly

I don't get charged for being connected (attached), only for data.

do you know how to send an e-mail to Gmail or Yahoo account via GPRS?

I use Sagem HiLo module; it is very easy just AT commands, see: http://www.libelium.com/tienda/catalog/images/arduino/AT_Commands.pdf, Appendix 9.

Do you guy have any idea about designing power source for GPRS modem & microcontroller via Li-Ion (Li-Po) battery and solar power?

TPS61200 Solar LiPo charger questions
http://e2e.ti.com/support/power_management/battery_management/f/179/t/23307.aspx

How to design a Li-Ion battery charger to get maximum power from a solar panel
http://www.powermanagementdesignline.com/howto/197008555

Don't forget GSM is TDMA so you'll only be using 2A (max) during your tx timeslot; if you're using 1 timeslot and CS-1 coding then you'll move about 1,000 bytes in a second but your radio will only have been transmitting for 1/8 second.

[Ichan]

Do you guy have any idea about designing power suppy for GPRS modem & microcontroller with Li-Ion (Li-Po) battery and solar power?

I have no experience with a real solar application, until now power source is never be a problem - the battery is only for backup. How about digging more deep on the SIM300 Li-ion charging function? Perhaps the people on Simcom already have a solution for this.

And I haven't had any idea to solve this yet

The MAX1758 can reduce the charging current (to the battery) if the current to the load (equipment) is go above a predefined limit. As an idea, the microcontroller can control the load sharing itself by measuring the condition of battery and solar panel, and then switch between that two as required.

-ichan

[blacknight72]

How to design a Li-Ion battery charger to get maximum power from a solar panel
http://www.powermanagementdesignline.com/howto/197008555

After read this, I think I've found a solution. BQ24071 of Texas Instrument may be suitable for my application:
- It has different pins for charging battery and loading system.
- It supports output current up to 2-4A (this will fit 2A peak current of SIM300D)
Do I have sth wrong?


By the way, let's consider about solar panel. Solar panel 6V/2.5W is the only one that output 6V I can find in my location (so, maximum current is about 410mA in theory and about 200-300mA in real). How long does it take to charge a 1200mAh Li-Po battery to full capacity? Is this solar panel okay, then?

Otherwise, I have to choose a 12V solar panel and a regulator will be need to output 6V for charging. In this case, how much power is enough (5W, 10W ...)

Another thing is regulator for microcontroller, would you recommend a selection for this (output ~3.3V from 4.4V) (saving as much as power is good)?

[Top]

BQ24071 of Texas Instrument may be suitable for my application

Looks ideal!

You can use 6 or 12 volt panel, set DPPM for your panel and no input regulator; BQ24071 max IN is 18 volt.

You need to work out how much power you'll use in a 24 hour period and then size your panel to replace it during daylight hours.

Any micropower low-dropout voltage regulator will do the job; LP2980, LP2981, etc.

LP2980 Micropower 50 mA Ultra Low-Dropout Regulator
http://www.national.com/mpf/LP/LP2980

LP2981 Micropower 100 mA Ultra Low-Dropout Regulator
http://www.national.com/mpf/LP/LP2981

[blacknight72]

You can use 6 or 12 volt panel, set DPPM for your panel and no input regulator; BQ24071 max IN is 18 volt.

I almost forgot this, thanks so much. So the solar panel problem in selection was solved.

Any micropower low-dropout voltage regulator will do the job; LP2980, LP2981, etc.

LP2980 Micropower 50 mA Ultra Low-Dropout Regulator
http://www.national.com/mpf/LP/LP2980

LP2981 Micropower 100 mA Ultra Low-Dropout Regulator
http://www.national.com/mpf/LP/LP2981

Because the microcontroller may need more than 100mA, so I think I can not use these regulator.
How about using MCP34063 for this?

[Ichan]

TLV1117 or similar is commonly used, 800mA output.

I have SIM548 still in box and a 12V solar panel too, i think i am gonna try them, but PIC18F4550 is my choice because of the usb feature it have.

-ichan

[blacknight72]

I often use 1117, too. But it can only output 3.3V if Vin > 4.7-5V.

I've sent data by SIM548 successfully, so if you need anything, I think I can help.
May I ask you why do you wanna use USB function in this app?

[Top]

Because the microcontroller may need more than 100mA

Why 100mA? You only need to budget 10-20mA for your microcontroller for this simple application. An AVR will run directly from your 4.4 volt power rail; saving you another voltage regulator and no worries about comms level shifting.

AVR® 8-Bit RISC - picoPower Technology
http://www.atmel.com/products/AVR/default_picopower.asp

[Ichan]

I've sent data by SIM548 successfully, so if you need anything, I think I can help.

Sure I will, thank you very much. This will be a slow journey as i will switch to this task when i get bored with my current main task.

May I ask you why do you wanna use USB function in this app?

The USB needed to:
a. Bootloading the firmware.
b. Downloading the data to pc on "off-line mode".
c. Changing device parameters via pc.

As Top said, other reason to choose this PIC is it work on 2 - 5.5V range, i don't need any OS for this and i think it spec'd perfectly for my app.

-ichan

[blacknight72]

That's a good idea.
I intended to use RS232 for those. PIC32MX has both USB Host & Client so it't will be more flexible. Only one problem is operating voltage .

I am trying to buy some BQ24070 but I can not find a place that can sell small quantity (5-10 devices). Do you know some?
I have friends in Singapore, Malaysia, Taiwan.

[Ichan]

I usually buy my prototyping requirement from Digikey or Mouser, just check them - Mouser has bq24072 in stock but bq24070 is On-Order Status.

I'm on the way gathering information on Simcom built-in charging function, if possible i would prefer to use it - it will mean a lot of saving.

-ichan

[Top]

I am trying to buy some BQ24070 but I can not find a place that can sell small quantity (5-10 devices). Do you know some?

Farnell Singapore has them in stock:

TEXAS INSTRUMENTS - BQ24070RHLTG4 - CHARGER, LI-LON, 4.4V, SMD, QFN-20
http://sg.farnell.com/jsp/displayProduct.jsp?sku=1494884

I usually buy my prototyping requirement from Digikey or Mouser, just check them - Mouser has bq24072 in stock but bq24070 is On-Order Status.

For you maybe TI BQ24032A more suitable; has 2 inputs, one for your panel and another to recharge from USB.

BQ24032A Dual Input Li-Ion Charger with Dynamic Power Path
http://focus.ti.com/docs/prod/folders/print/bq24032a.html

In stock at Digi-Key, Digi-Key Part Number: 296-18285-1-ND

Don't forget TI ship free samples if you're not in a hurry and only need a few!

[blacknight72]

I've bought some of BQ24070 from Farnell (I can't get free samples from my country).

There is another thing I wanna ask is Cell phone's battery's pins.
The battery has 3 pins (2 pins for power and 1 pin in the middle). I don't know what is the pin in the middle. What is it used for?

I also having problem in connecting battery's pins to circuit. Do you have any ideas?

[Ichan]

Middle pin mostly one of the internal thermistor pin, the other pin connected to ground, measure with ohm meter between this pin and ground (negative) pin - around 10 K value is common.

I solder several pins of single row header connector directly on to the battery tab, brute but works perfectly 

After breaking the cover of several cell phone batteries i found that the tab is not directly connected to the battery, the tab is a part of the protection circuit pcb. The negative side of course, i cannot put the battery back to my cell phone... 

-ichan