bq2057

The BENCHMARQ bq2057 series advanced Li-Ion linear charge-man-agement ICs are designed for cost-sensitive and compact portable electronics. They combine high-accuracy current and voltage regulation,battery conditioning, temperature monitoring, charge termination,charge-status ndication, and AutoComp charge-rate compen-sationinasingle8-pinIC.


The bq2057 continuously measures battery temperature using an external thermistor. For safety reasons,the bq2057 inhibits charge until the battery temperature is within user-defined thresholds. That then charges the battery in three phases: conditioning, constant current, and constant voltage. If the battery voltage is below the low-voltage threshold VMIN, the bq2057 trickle-charges to condition the battery. The conditioning charge rate is set at 10% of the regulation current. The conditioning current also minimizes heat dissipation in the external pass-element during theinitialstageofcharge.


After conditioning, the bq2057 applies a constant current to the battery. An external sense-resistor setsthe magnitude of the current. The sense-resistor can be on either the low or the high side of the battery without additional components. The constant-current phase continues until the  attery reaches the charge-regulationvoltage.


The bq2057 then begins the constant-voltage phase. The accuracy of the voltage regulation is better than ±1% over the operating-temperature and supply-voltage ranges. For single and dual cells with either coke or graphite anodes, the bq2057 is offered in four fixed-voltage versions:4.1V, 4.2V, 8.2V, and 8.4V. Charge stops when the current tapers to the charge termination threshold, VTERM. That automatically restarts the charge if the battery voltage falls below the VRCH threshold.


The designer of bq2002C also may use the AutoComp feature to reduce charging time. This proprietary technique allows safe and dynamic compensation for the internal impedance of thebatterypackduringcharge.