BQ40Z50-R2 Datasheet, PDF (35/51 Pages) Texas Instruments – 1-Series, 2-Series, 3-Series, and 4-Series Li-Ion Battery Pack Manager

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bq40z50-R2
SLUSCS4 – JUNE 2017
9.2.2.3.1 Cell and Battery Inputs
Each cell input is conditioned with a simple RC filter, which provides ESD protection during cell connect and acts
to filter unwanted voltage transients. The resistor value allows some trade-off for cell balancing versus safety
protection.
The integrated cell balancing FETs enable the AFE to bypass cell current around a given cell or numerous cells,
effectively balancing the entire battery stack. External series resistors placed between the cell connections and
the VCx I/O pins set the balancing current magnitude. The internal FETs provide a 200-Ω resistance (2 V < VDS
< 4 V). Series input resistors between 100 Ω and 300 Ω are recommended for effective cell balancing.
The BAT input uses a diode (D1) to isolate and decouple it from the cells in the event of a transient dip in voltage
caused by a short-circuit event.
Also, as described in High-Current Path, the top and bottom nodes of the cells must be sensed at the battery
connections with a Kelvin connection to prevent voltage sensing errors caused by a drop in the high-current PCB
copper.
Figure 32. Cell and BAT Inputs
9.2.2.3.2 External Cell Balancing
Internal cell balancing can only support up to 10 mA. External cell balancing provide as another option for faster
cell balancing. For details, refer to the application note, Fast Cell Balancing Using External MOSFET (SLUA420).
9.2.2.3.3 PACK and FET Control
The PACK and V_CC inputs provide power to the bq40z50-R2 device from the charger. The PACK input also
provides a method to measure and detect the presence of a charger. The PACK input uses a 10-kΩ resistor;
whereas, the V_CC input uses an internal diode to guard against input transients and prevent a mis-operation of
the gate driver during short-circuit events.
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