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Problems with Battery Protection Circuit

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Kian

Member
Hi all,

I am designing a circuit that runs on a single rechargeable lithium ion polymer battery. The battery does not come with any inbuilt battery protection circuit so I implement my own protection circuit based on S-8261. I followed the same exact design in my application:




The battery is connected to VDD and VSS of the S-8261. And I am using EB+ and EB- as the VCC and GND of my circuit. I also have a 3.3V LDO voltage regulator connected to EB+ and EB-.

The problem I am facing now is that when the battery is connected, there is no voltage on EB+ and EB-. Only when I short circuit battery negative terminal to EB- momentarily , then everything will start working normally. I can remove the short circuit and there is a voltage across EB+ and EB-. I don't know what is the cause of it. Can anyone help or advise?
 

cowboybob

Well-Known Member
Most Helpful Member
What are you using as the battery charging source/circuit?

From your description, your assuming the EB+ and EB- are the output of the circuit, rather than the charger input points.
 

Kian

Member
Hi,

I am using a lipo charger IC, MCP73831. It is connected to EB+ and EB- to charge the battery.
 
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cowboybob

Well-Known Member
Most Helpful Member
... And I am using EB+ and EB- as the VCC and GND of my circuit. I also have a 3.3V LDO voltage regulator connected to EB+ and EB-. ...
I don't understand why you have your circuit connected this way.What are you using as the charger?

Please give us a complete schematic of your entire circuit as wired.
 

Pommie

Well-Known Member
Most Helpful Member
I recently built a circuit using the same charger but with a boost regulator for the output. The battery I used was a 1AH Lipo from Sparkfun. The battery has built in protection to stop over discharging. I posted the schematic in this thread - is yours similar?

Mike.
 

Kian

Member
Hi,
I am quite sure my circuit is correct. When you buy a lipo battery with built in battery protection, it has almost the same circuit inside and the two wires coming out from the lipo battery is connected to the + terminal of the battery (red wire) and the EB- (black wire).

My complete circuit is given below:


 
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Kian

Member
I have limitations with the thickness of the battery and none of the lipo batteries in the market with built-in battery protection fits my requirements. I will need a bare lipo battery without the protection circuit and I need to put the battery protection circuit on the PCB instead.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I have limitations with the thickness of the battery and none of the lipo batteries in the market with built-in battery protection fits my requirements. I will need a bare lipo battery without the protection circuit and I need to put the battery protection circuit on the PCB instead.
The board and circuit I posted is for unprotected LiPo's - either use the small boards, or copy it to your own PCB :D
 

Kian

Member
But if I followed the reference design, it should work! But it isn't. Is there any way to troubleshoot this?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
The pin numbers on the dual FET seem to be different to those on the circuit I posted, you might like to check which is correct.

You're also a little hopeful if you think that datasheets are always correct!.
 

alec_t

Well-Known Member
Most Helpful Member
:confused: I don't understand your use of the S8205A if you have a single-cell battery. That IC is intended for a 4-cell or 5-cell battery.
 

alec_t

Well-Known Member
Most Helpful Member
Ah, seems like the same code is used for two different things :rolleyes:. Here's the IC.
 
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