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Front-end ICs protect systems during charging

Posted: 10 Sep 2007 ?? ?Print Version ?Bookmark and Share

Keywords:safety circuits? battery charger front-end ICs?


Texas Instruments Inc. has introduced a family of battery charger front-end ICs, which dramatically increases protection when charging a cellphone or other portable electronic device. The 2mm x 2mm safety circuits protect a system from input overvoltage, overcurrent and battery overvoltage conditions, which may result from a power spike during charging, or a defective or incorrect wall adapter.

"Adding power protection to a handheld device helps safeguard end users against accidental fault conditions, which reduces the number of customer end-equipment returns," said Masoud Beheshti, director of TI's battery charge management business. "This unique charger front-end circuit provides three solid levels of protection to provide the maximum amount of safety when charging a handheld device."

The first member of TI's bq243xx family of charger front-end circuits with integrated FETs, the bq24314, adds extra protection to a lithium battery when a charger circuit fails due to a fault condition. The protection IC can report status of the fault to the host processor, such as TI's new DM355 processor based on DaVinciTM technology or an application processor from the OMAP 3 product family, allowing the host processor to apply additional corrective actions.

Key features
Input overvoltage conditions are caused by steady-state or transient voltage events, such as hot-plugging a charged adapter; using a non-regulated or incorrect adapter; or load transients. Any of these events can increase or spike the voltage applied to the device and potentially damage the host system. The bq24314 detects the over-voltage level and effectively disconnects the input to the charger to protect the device. The device features an input overvoltage threshold of 5.85V. Another version of the circuit, the bq24316, supports up to 6.8V.

Input over-current conditions can occur in integrated power management devices that incorporate a battery charger, which have a direct connection from the input to the system's bus voltage. Often there is no protection from pulling excessive current from the adapter to the system. The programmable bq24314 limits the input current by sensing and regulating its integrated MOSFET to ensure the system does not pull an excessive amount of current.

Potential hazardous events may occur if single-cell, Li-ion and Li-polymer batteries are over-charged beyond their float voltagetypically around 4.2V. Because of this, portable designers currently seek redundant safety measures to ensure battery safety and compliance. The bq24314 offers a second level of protection that helps monitor the battery's voltage, and if an overvoltage is detected, interrupts the input charging source.

In summary, the key technical features of the bq24314 and bq24316 include:

  • 30V maximum input voltage

  • Integrated power FET and current sensor that supports up to 1.5A input current

  • Less than 1?s response time against input overvoltage

  • Input overvoltage protection threshold at 5.85V (bq24314) or 6.8V (bq24316)

  • High immunity against false triggering due to current transients

  • Status indication - fault condition

  • Thermal shutdown

The bq24314 and bq24316 are available today in volume. Both devices come in a tiny 8-pin, 2mm x 2mm small-outline, Pb-free (SON) package. Pricing for both in 1,000-piece quantities is at 75 cents. Evaluation modules of the bq24314 and bq24316 are also available.

In Q4, TI plans to introduce new bq24300 charger front-end protection ICs. Featuring a fixed input over-current protection threshold of 300mA, and input over-voltage protection threshold at 10.5V, the bq24300 devices target low-power applications, like Bluetooth headsets. The bq24300 acts as a linear regulator by managing the output to 5.5V (or 4.5V with the bq24304) for voltages up to the input overvoltage threshold. Additionally, a bq24300 circuit can protect against reverse polarity caused by a faulty adaptor using an optional external P-channel MOSFET.

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