BQ40Z60_16 Datasheet, PDF (25/47 Pages) Texas Instruments – Programmable Battery Management Unit

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bq40z60
SLUSAW3C – DECEMBER 2014 – REVISED JULY 2015
Feature Description (continued)
The charger maintains a cycle-by-cycle current limit by sensing across a resistor in series with the inductor
(shown in Figure 6 as R_CHG). In precharge and constant voltage, the DC current is regulated by sensing the
current across the sense resistor at the bottom on of the cell stack. When the charger is enabled, the initial
current is set for either the Precharge or Constant Current/Constant Voltage (CC/CV) value, based on the
minimum cell voltage. Once the charger enters CONSTANT CURRENT mode, the temperature and maximum
cell voltage-adjusted–charging current is set, and the voltage output of the charger is automatically regulated to
maintain the current across RCHG. Once the temperature-adjusted voltage is reached by the charger output, the
current starts to taper.
Throughout the charge cycle, the current available from the charger is limited by the ChargingCurrent() value.
The system draws more current, however, with the battery supplementing the difference. Once battery charging
is terminated, the charger is capable of supplying all of the current defined by the Advanced Charge
Algorithm:Maximum Current Register value. Refer to the bq40z60 Technical Reference Manual (SLUUA04) for
more information.
Figure 6 shows the system power path with the adaptor current and battery current overlaid. Further information
is available in Application and Implementation.
Power
Adapter
IADAPTER
Path
AC
FET
R_CHG
R₁
R₂
IBAT
Path
ACFET
ACP
VCC HIDRV
LODRV HSRP HSRN FB
Charger
Current Sense
Charger PWM
Control
Zero Volt
Charge Enable
GND
Protection
FET
Control
DSG
CHG
BAT
DSG
FET
CHG
FET
SRN
SRP
Pack–
Figure 6. Power Path Overview
9.3.3.1 Precharge Modes
The charge controller is designed to allow for both internal precharge control and external precharge control. The
device can operate in precharge with external FETs and a current limiting resistor. Refer to the bq40z60
Technical Reference Manual (SLUUA04) for more information.
9.3.3.2 Zero-Volt Charge Support
This mode of operation is similar to PRECHARGE mode switched charging, but with the charge FET operation in
the saturation region. The NVDC out is connected to the CHG gate drive output internally to allow for precharge
current from the charger through the CHG FET. This current is limited based on the value of the external R_sense
(10-mΩ resistor the lowest precharge current = 200 mA). This will increase the power dissipation of the charge
FET and will require thermal heat management and protection to ensure correct operation.
9.3.3.3 Charge Termination
Once the highest cell voltage reaches the value specified in the data flash, the charger output voltage will no
longer increase and the current will start to taper. Once the highest cell voltage is within the Charge Term
Voltage window and the measured current is below Charge Term Taper Current for 40 s or more, the charger
will terminate by disabling the CHG FET and setting the appropriate flags. Refer to the bq40z60 Technical
Reference Manual (SLUUA04) for more information.
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