BQ25050 Datasheet, PDF (15/28 Pages) Texas Instruments – 1A, Single-Input, Single Cell Li-Ion Battery Charger with 50-mA LDO, External Power Path

bq25050
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Charger Operation With External Power Path Control Mode Disabled (BGATE = VSS)
PRECHARGE CC FAST CHARGE
CV TAPER
SLUSA33 – MARCH 2010
V_OUT(REG)
I_FASTCHG
Battery
Current
V_LOWV
I_PRECHG
I_TERM
Battery and
Output
Voltage
CHG = Hi-Z
Figure 23. Charging Cycle with External Power Path Control Disabled (BGATE = VSS)
Precharge Mode (V_BAT ≤ V_LOWV)
The bq25050 enters precharge mode when V_BAT ≤ V_LOWV. Upon entering precharge mode, CHG goes low and
the input current limit is set to I_PRECHARGE. With BGATE connected to GND, the system output is connected to the
battery and therefore the system voltage is equal to the battery voltage. During precharge mode, the input
current is regulated to 50mA and as such, only loads up to 50mA are supported.
Normal CC/CV Mode
Once V_BAT > V_LOWV, the bq25050 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 VBAT(REG), the bq25050 enters constant voltage (CV) mode where
V_BAT is regulated to VBAT(REG) and the current is reduced. Once the input current falls below the termination
threshold (I_TERM), CHG goes high impedance but the system remains charging and regulates the output to
V_BAT(REG).
Charge Current Translator (IMON)
When the charger is enabled, internal circuits generate a current proportional to the charge current at the IMON
input. The current out of IMON is 1/1000 (±10%) of the charge current. This current, when applied to the external
charge current programming resistor, R1 (see Figure 1), generates an analog voltage that can be monitored by
an external host to calculate the current sourced from BAT. Connect a 1kΩ resistor from IMON to VSS. The
voltage at IMON is calculated as:
V_IMON = 1_IN × 1 V/A
Using this output allows for the host to calculate the actual charging current and therefore perform more accurate
termination. The input current to the system must be monitored and subtracted from the current into the bq25050
which is show by V_IMON.
Input Over Voltage Protection
The bq25050 contains an input over voltage protection circuit that disables the LDO output and charging when
the input voltage rises above V_OVP. This prevents damage from faulty adapters. The OVP circuitry contains an
deglitch that prevents ringing on the input from line transients from tripping the OVP circuitry falsely. If an adapter
with an output greater than V_OVP is plugged in, the IC completes power up and then shuts down if the voltage
remains above V_OVP after the deglitch. The LDO remains off and charging remains disabled until the input
voltage falls below V_OVP.
Copyright © 2010, Texas Instruments Incorporated
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