Hi,
I am using the LTC3440 to convert the voltage from a LiPo Battery into a stable 3.3V to power an IoT device. I made the design of the power section following the typical application diagram of the datasheet, as you can see in the following diagram.
After manufacturing the PCBs, I did some tests and everything works fine, the DCDC output remained stable at 3.3v and with the system working the input current was around 50mA (for 2 days).
Next day, after a thunderstorm night (I don't know if this had something to do, but I can't think of anything else, because I didn't change anything in the test setup from one day to the other), I tested again with a fully charged 4.2V battery. This time the device wasn’t working, the LTC was getting too hot and had an excessive current draw of about 500mA with 1.8V output.
Trying to see what could have failed, I realize that GND-SW1 and GND -SW2 where shorted (~5ohms resistance). At first, I thought it might be the Schottky diodes that were shorted, but after carefully desoldering the LTC from the PCB in order to make more realistic measurements I realize that SW1 (pin of the LTC3440) was shorted to ground.
Looking at the logic diagram of the datasheet, I think the problem may be the driving SW B mosfet which is shorted, but I don't know what could have been the reason for that.
With the LTC desoldered I tested the rest of the circuit feeding it directly with a 3.3v power supply and it was working correctly (current draw of about 50mA).
I hope you can help me,
Thanks
