BQ24171 Datasheet, PDF (16/35 Pages) Texas Instruments – JEITA Compliant Stand-Alone Switch-Mode Li-Ion and Li-Polymer Battery Charger with Integrated MOSFETs and Power Path Selector

bq24171
SLUSAF2A – FEBRUARY 2011 – REVISED MAY 2011
DETAILED DESCRIPTION
Regulation Voltage
V_RECH
I _CHRG
Precharge
Current
Regulation
Phase
Fastcharge Current
Regulation Phase
Fastcharge Voltage
Regulation Phase
Charge
Current
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Termination
V_LOWV
10% I_CHRG
Charge
Voltage
Precharge
Timer
Fast Charge Safety Timer
Figure 17. Typical Charging Profile
BATTERY VOLTAGE REGULATION
The bq24171 offers a high accuracy voltage regulator on for the charging voltage.
The bq24171 uses external resistor divider for voltage feedback and regulate to internal 2.1V voltage reference
on FB pin. Use the following equation for the regulation voltage for bq24171:
VBAT
= 2.1 V ´
é
êë¹⁺
R2 ù
R1 ^úû
(1)
where R2 is connected from FB to the battery and R1 is connected from FB to GND.
BATTERY CURRENT REGULATION
The ISET input sets the maximum charging current. Battery current is sensed by current sensing resistor RSR
connected between SRP and SRN. The full-scale differential voltage between SRP and SRN is 40mV max. The
equation for charge current is:
I_CHARGE =
V_ISET
20 ´ R_SR
(2)
The valid input voltage range of ISET is up to 0.8V. With 10mΩ sense resistor, the maximum output current is
4A. With 20mΩ sense resistor, the maximum output current is 2A.
The charger is disabled when ISET pin voltage is below 40mV and is enabled when ISET pin voltage is above
120mV. For 10mΩ current sensing resistor, the minimum fast charge current must be higher than 600mA.
Under high ambient temperature, the charge current will fold back to keep IC temperature not exceeding 120°C.
16
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