June Birth Magoncia

user Electronics Engineer

city Innovuze Solutions, Inc.


  • Single Cell Li-Ion/Li-Po Battery Charger

  • Created: Jan 26, 2016

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Description

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Summary

This reference design features the BQ24100 device intended for charging lithium-ion and lithium-polymer batteries. The BQ24100 device regulates voltage and current precisely. It can run in stand-alone mode or can be controlled externally by a system. The device circuitry also includes some monitoring and safety features such as current sensing, battery temperature monitoring, thermal shutdown, etc. The internal power FETs of BQ24100 can charge batteries up to 2A rate through the 476150001 battery connector.


In this reference design, the BQ24100 acts as a stand-alone single cell li-ion or li-polymer battery charger. The input voltage in this circuit is 16V. The capacitors C1 and C3 filter the input voltage, while LED1 indicates if the input voltage is ON or OFF. The LEDs (LED2 and LED3) serve as a charging status indicator. When LED3 is ON, the battery is still being charged. If LED3 turns OFF and LED2 turns ON, the charging process is complete. If both LEDs are OFF, it could be a battery absent, overvoltage, sleep mode, timer fault, or charge suspend status. The charge time is determined by the value of capacitor C2. The resistor R4 determines the charge current during fast charge phase, while R5 sets the precharge/termination current level. The value of L1 and C5 determines the maximum output current of the charger as well as the resonant frequency. The resistor R6 serves as a reference for the internal current sense amplifier of BQ24100 to monitor the charge current and to decide whether to enable or disable fast charging. The resistors R7 and R8 acts as a voltage divider to provide voltage to the internal thermistor of the battery compatible to the voltage level used by the temperature sensor of BQ24100.


The circuit in this design is cost-effective for charging batteries such as lithium-ion and lithium-polymer. It can be used to charge batteries used in handheld products, industrial and medical equipment, portable media players, etc. The BQ24100 device can handle inputs with a minimum voltage of 4.35V and a maximum voltage of 20V. If ever the input voltage is changed, recalculation must be done to obtain the exact value of the external components. The current capacity of the input supply must also exceed the maximum output current that the BQ24100 device can provide.

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