Problems with Battery Protection Circuit

[Kian]

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]

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]

Hi,

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

 

[cowboybob]

... 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]

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]

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:

 

[Nigel Goodwin]

Why not just buy a ready built charger/protection board - such as these:

https://www.banggood.com/USB-Lithiu...rd-With-Charging-And-Protection-p-924048.html

Here's the schematic of it:

 

[Kian]

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]

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

 

[Kian]

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

 

[Nigel Goodwin]

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]

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.

 

[Nigel Goodwin]

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.

It's just a dual FET (not an IC at all), and equally suitable for a single cell - and used in the board I linked to.

 

[alec_t]

Ah, seems like the same code is used for two different things . Here's the IC.