BQ29200: bq29200

Hi Mario,
The bq29200 is expected to be connected to the cells at all times. It operates both during charge and discharge. Its over voltage detection is always enabled. The cell balancing can be enabled by a circuit such as an MCU as you show. When enabled the bq29200 will balance when the voltages differ by more than the threshold, they do not check for charge or discharge. Since the cell voltages may deviate more toward the end of discharge, you may want to disable balancing when the voltage is low.

Hi Mario,
The bq29200 is a secondary protector but it expects the cells to be always attached. If the bq29200 was connected to the protected cell and it protected from UV with a load the voltage would reverse on the inputs to the bq29200 for the protected cell. This would violate the abs max rating and is not recommended.

Hi Mario,

If the cell protected during charge the bq29200 would likely be safe since the charge voltage is 8.2V.  The concern is when the battery protects from a current or under voltage condition with load, the voltage will reverse to the inputs.  See the markup on the original schematic below.

Hi Mario,
What protections you need depends on your system requirements from your industry or system architecture. Many systems will use FETs to cut off the charge or discharge when the battery is operated outside the parameters set by the battery system designer. In our product line when protection is needed on a single cell it is may be provided by the bq2970 which will operate like your protected cell. When 2 cells are needed to be balanced and UV and current protections are handled in another circuit the bq29200 is available although the OV thresholds are more of secondary levels. When 2 cells need full featured protection the band balancing are needed with 2 cells it comes with a gauge such as the bq28z610, bq4050 or bq40z50-R1. The bq29200 could still be a secondary protector if desired but the balancing would not be needed and there are other options for a secondary protector.