STNS01 occasionally getting hot while charging

[florianpabst9]

Posted on June 01, 2016 at 13:15

Hi to all,

i implemented the STNS01 on a small wireless sensor. The STNS01 is charging a coin cell type LIR2440. The schematics for the battery charging part of the sensor are attached below. Usually the charging process works without problems. But a few times i had the problem that the STNS01 produced a lot of heat and the CHG status LED was flashing. Unfortunately i can't tell if the CHG status LED was flashing before the STNS01 was getting hot or if the STNS01 was heating and than the LED started flashing. When i removed the power supply and let the chip cool down a bit, i was able to do another charing process without problems. The problem that the STNS01 got hot, occured maybe 5 times out of 500 charging processes. My question is now, why is the STNS01 getting hot sometimes and charging without problems for the rest of the time? I can't find a reason for this, but i need to eliminate this behavior. Best Regards Florian

[Mathis Huther]

Posted on April 24, 2017 at 10:02

Hi Florian,

   you applied the USB bus voltage directly to the CEN pin - which is not allowed! This pin has an internal 500k pullup to the 3.1V LDO (see Table 3) and is rated 4.0V maximum (see Table 4). My guess: the 5 times when your STNS01 got hot the USB voltage was a little bit higher than the other 495 times - e.g. because of a lower count of connected devices drawing current. Just leave the CEN pin floating or connect it directly to LDO as described on page 14 of the datasheet and everything should work fine

Kind regards,

   Mathis