Battery Protection circuit 1

[jamesnguyen]

Hi everyone,

I implemented a battery protection circuit as suggested by the S-8242B protection IC's datasheet and ran into a problem. I then simulated the circuit in LTspice and confirmed that the problem actually exists.

As shown in the attached picture, the two back-to-back N MOSFET are supposed to disconnect the battery when the battery voltage is too low (DO output goes Low) and when the voltage is too high (CO output goes Low). The problem is that when CO goes low, FET2 does not turn off.

I did a quick test in LTspice and found that the current flows through R1 is about 1Amp. What's the problem? Should M2 MOSFET be off?

The battery protection IC's datasheet is here:

http://datasheet.sii-ic.com/en/battery_protection/S8242B_E.pdf

Thank you in advance!
James

 

[zappedagain]

Did you read through the notes on p. 18 of the S8242B data sheet? Maybe the Vth =1.0 of the SI4410 doesn't meet the requirements defined in Note 2.

John D

 

[IRstuff]

I don't think your SPICE model is representative of the canonical circuit. Your model allows the source of M2 to rise well above ground; this is the fundamental problem, coupled with the fact that M3 is turned ON, therefore allowing current to flow through the substrate of M2 into its drain diode, then through M3. Assuming that M2 is correlated with FET2, you can see that the actual circuit would never have EB- go anywhere close to EB+

TTFN

FAQ731-376

 

[jamesnguyen]

Thank you for your help. I can understand that with M3 turned on, current flows from M2 to M3 through its drain diode.

However, I don't see how my model is any difference from the suggested circuit. The Ground of M2 and M3 FETs is the same as the battery's ground. Could you please help to shine some lights?

Best regards,
James