I have been designing a battery management system for several months now and have come up against a strange problem.
I have set the three multiturn pots, R2 R3 and R4 so that overvoltage triggers with a battery voltage of 4.2, undervoltage of 3.4 and a balance voltage of 4v
When I apply power and the battery voltage is below 4v, both the overvoltage and undervoltage outputs are triggered and in some cases the balancing will trigger also. If the supply voltage is above 4v, they don't trigger when the power is applied and the module works as it should across the entire operating voltage range of a lithium ion cell. I am beginning to suspect that this may be due to my poor choice of comparator, the LM239DT. I am using a 1.225v voltage reference and the common mode voltage range of the comparator is VCC+ -1.5 VCC + -2 as per the datasheet with a supply voltage of 30v. The confusing thing is that not all of the boards have this problem despite being exactly the same so I am not too sure what to do. It would seem like the comparator on the faulty boards is requiring a higher voltage to start up properly.
