BQ25070 Datasheet, PDF (10/21 Pages) Texas Instruments – 1A, Single-Input, Single-Cell LiFePO4 Linear Battery Charger with 50mA LDO

bq25070
SLUSA66 – JULY 2011
www.ti.com
DETAILED FUNCTIONAL DESCRIPTION
The bq25070 is a highly integrated LiFePO₄ linear battery charger targeted at space-limited portable applications.
It operates from either a USB port or AC Adapter and charges a single-cell LiFePO₄ battery with up to 1A of
charge current. The 30V input voltage range with input over-voltage protections supports low-cost unregulated
adapters.
The LiFePO₄ charging algorithm removes the constant voltage mode control usually present in Li-Ion battery
charge cycles. Instead, the battery is charged with the fastcharge current to the overcharge voltage and then
allowed to relax to a lower float charge voltage threshold. The removal of the constant voltage control reduces
charge time significantly. During the charge cycle, an internal control loop monitors the IC junction temperature
and reduces the charge current if an internal temperature threshold is exceeded. The charger power stage and
charge current sense functions are fully integrated. The charger function has high accuracy voltage and current
regulation loops, and charge status display.
CHARGING OPERATION
The bq25070 uses a charge algorithm that is unique to LiFePO₄ chemistry cells. The constant voltage mode
control usually present in Li-Ion battery charge cycles is eliminated. This dramatically decreases the charge time.
When the bq25070 is enabled by CTRL, the battery voltage is monitored to verify which stage of charging must
be used. When V_BAT < V_LOWV, the bq25070 charges in precharge mode; when V_BAT > V_LOWV, the normal charge
cycle is used.
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 13. Typical Charging Cycle with Minimum System Voltage Enabled
Precharge Mode (V_BAT ≤ V_LOWV)
The bq25070 enters precharge mode when V_BAT ≤ V_LOWV. Upon entering precharge mode, the battery is charged
with a 47.5mA current and CHG goes low.
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Copyright © 2011, Texas Instruments Incorporated