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We have designed a changing module using BQ2057WSN IC to charge a 7.4V, 6600mAH Li-ion battery. My supply power is 12V,2A SMPS. I have set my charging current to 600mA. The battery is charging, but a high amount of heat is generating (dissipating) through the transistor, Q1. (around 80 degree Celsius). But in some of the I found that the battery is not charging. I have measured the input power supply voltage and found it as 12V which is fine. Then I have measure the battery float voltage. I have found that in some of the circuits it is 0.5V, in some of the circuits it is 3V and in some of the circuits it is 11.7V. I have checked continuity and nothing is short. So, what could be possible reasons of getting such unexpected battery float voltage? Is there any flaws in my design or the IC is faulty ( But remember IC is not showing any short circuit).

I also found that out of these circuits,in some circuits , the battery was charging but a high amount of heat was generating. But now it is not charging and giving unexpected battery float voltage as I already mentioned. Is there any possibility that the heat can damage the charging IC? What are the possible reason that in some of the circuits the float voltage is uncontrolled?Schematic

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