This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

[FAQ] BQ25890: Why does the LED connected to STAT pin flashes and the SYS voltage unstable when battery is not connected for BQ25890, BQ25890H, BQ25892, BQ25895, BQ25895M, BQ25896, BQ25898, BQ25898D, BQ25898C, BQ24190, BQ24192, BQ24192I, BQ24193, BQ24195,

Part Number: BQ25890
Other Parts Discussed in Thread: BQ24190, BQ25898, BQ24296, BQ24192I, BQ25895, BQ25896, BQ24193, BQ24192, BQ24292I, , BQ24295, BQ24298, BQ25898C, BQ25898D, , BQ24259, BQ25895M, BQ25892, BQ24296M, BQ24195, BQ24196, BQ24297, BQ24195L

Hi,

The LED on the battery charger evaluation module (EVM) flashes and the SYS voltage is not stable when the battery is not connected. This applies for BQ25890, BQ25890H, BQ25892, BQ25895, BQ25895M, BQ25896, BQ25898, BQ25898D, BQ25898C, BQ24190, BQ24192, BQ24192I, BQ24193, BQ24195, BQ24195L, BQ24196, BQ24292I, BQ24295, BQ24296, BQ24297, BQ24296M, BQ24259, BQ24298. The reasons are listed below:

 

  • The battery charger IC does not detect the battery’s connection. The charger sees the capacitor on BAT as a really small battery when a battery is not connected.
  • The charging function is enabled by default. The charger tries to regulate BAT pin voltage to charging voltage (VREG, e.g. 4.208V default). The BAT pin could be charged to VREG quickly as no battery connected and charger IC terminates the charging. After certain time, BAT pin voltage starts to drop due to the loading and the leakage on BAT. When the BAT pin voltage drops below the recharge threshold and the device starts to charger the BAT pin again. The charger status indicates swaps between charging in progress and charging complete. Therefore, the STAT pin blinks. The high fluctuating voltage on SYS pin is also related to the battery’s absence.
  • The frequent changes of charging status change could be observed as discussed by the thread below
  • If charging is set to disabled, either by pulling /CE pin high or set the register bit, the charger IC does not charge the BAT pin. The STAT pin will blink, SYS pin voltage is regulated at 150 mV typically above the minimum system voltage (VSYSMIN, e.g. 3.5V default) as well.