LTC040

Here's a question:

              The battery charging chip ltc4040 is used on the single board. When the single board does not need external power supply, one battery with a voltage of 3.3V is inserted into the charging port of battery charging chip ltc4040, that is, SW1 SW2. As a result, the ltc4040 will smoke and burn out. What is the reason for this. thank you!