BQ25071-Q1 Datasheet, PDF (13/22 Pages) Texas Instruments – Automotive Qualified

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8.4 Device Functional Modes
bq25071-Q1
SLUSCD6 – APRIL 2016
8.4.1 Charging Operation
The bq25071-Q1 uses a charge algorithm that is unique to LiFePO₄ chemistry cells. The current taper typically
seen as part of the constant voltage mode control usually present in Li-Ion battery charge cycles is replaced with
a floating regulation voltage with minimal charging current. This dramatically decreases the charge time. When
the bq25071-Q1 is enabled by EN, the battery voltage is monitored to verify which stage of charging must be
used. When V_(BAT) < V_(LOWV), the bq25071-Q1 charges in precharge mode; when V_(BAT) > V_(LOWV), the normal
charge cycle is used.
8.4.1.1 Charger Operation with Minimum System Voltage Mode Enabled
PRECHARGE
V_OUT(OVCH)
V_OUT(REG)
I_FASTCHG
Constant Current
Fast Charge
Float-Voltage
Regulation
CHG = Hi -Z
V_LOWV
I_PRECHG
Battery and
Output
Voltage
Battery
Current
Figure 10. Typical Charging Cycle with Minimum System Voltage Enabled
8.4.1.2 Precharge Mode (V_(BAT) ≤ V_(LOWV))
The bq25071-Q1 enters precharge mode when V_BAT ≤ V_(LOWV). Upon entering precharge mode, the battery is
charged with a 47.5 mA current and CHG goes low.
8.4.1.3 Fast Charge Mode
Once V_(BAT) > V_(LOWV), the bq25071-Q1 enters constant current (CC) mode where charge current is regulated
using the internal MOSFETs between IN and OUT. The total current is shared between the output load and the
battery. Once the battery voltage charges up to V_BAT(OVCH), the CHG output goes high indicating the charge cycle
is complete and the bq25071-Q1 switches the battery regulation voltage to V_BAT(REG). The battery voltage is
allowed to relax down to V_BAT(REG). The charger remains enabled and regulates the output to V_BAT(REG). If at any
time the battery falls below V_(RCH), the charge cycle restarts.
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