The bq24171 device is highly integrated stand-alone Li-ion and Li-polymer switched-mode
battery charger with two integrated N-channel power MOSFETs. The device offers a constant-frequency
synchronous PWM controller with high-accuracy regulation of input current, charge current, and
voltage. The bq24171 closely monitors the battery pack temperature and allows charge only in a
JEITA profile-compatible window with a lower charge rate at a low temperature and a lower charge
voltage at a high temperature. The bq24171 device charges the battery in three phases:
preconditioning, constant current, and constant voltage. The bq24171 charges up to 3-series cells
with an adjustable cell voltage.
The bq24171 charges the battery in three phases: preconditioning, constant current, and
constant voltage. The device is adjustable for up to three series Li+ cells.
Charge is terminated when the current reaches 10% of the fast charge rate. A programmable
charge timer offers a safety backup. The bq24171 automatically restarts the charge cycle if the
battery voltage falls below an internal threshold, and enters a low-quiescent current sleep mode
when the input voltage falls below the battery voltage.
The bq24171 features Dynamic Power Management (DPM) to reduce the charge current when the
input power limit is reached to avoid overloading the adapter. A highly accurate current-sense
amplifier enables precise measurement of input current from adapter to monitor overall system
The bq24171 device provides power path selector gate driver ACDRV/CMSRC on input NMOS
pair ACFET (Q1) and RBFET (Q2), and BATDRV on a battery PMOS device (Q3). When the qualified
adapter is present, the system is directly connected to the adapter. Otherwise, the system is
connected to the battery. In addition, the power path prevents battery from boosting back to the
The bq24171 charges battery from DC source as high as 17 V, including car battery. The
input overvoltage limit is adjustable through the OVPSET pin. The AVCC, ACP and ACN pins are 30-V
rating. When a high-voltage DC source is inserted, Q1 and Q2 remain off to avoid high voltage
damage to the system.
For 1-cell applications, if the battery is not removable, the system can be directly
connected to the battery to simplify the power path design and reduce the cost. With this
configuration, the battery can automatically supplement the system load if the adapter is
The bq24171 is available in a 24-pin, 5.5-mm × 3.5-mm thin QFN package.