BQ40Z50-R1 Datasheet, PDF (36/55 Pages) Texas Instruments – Li-Ion Battery Pack Manager

bq40z50-R1
SLUSCB3 – JULY 2015
www.ti.com
Figure 31. FUSE Circuit
When the bq40z50-R1 is commanded to ignite the chemical fuse, the FUSE pin activates to give a typical 8-V
output. The new design makes it possible to use a higher Vgs FET for Q5. This improves the robustness of the
system, as well as widens the choices for Q5.
9.2.2.3 Secondary-Current Protection
The bq40z50-R1 provides secondary overcurrent and short-circuit protection, cell balancing, cell voltage
multiplexing, and voltage translation. The following discussion examines Cell and Battery Inputs, Pack and FET
Control, Temperature Output, and Cell Balancing.
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 allow 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 1 kΩ 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.
36
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