Texas Instruments (TI) (NYSE: TXN) introduced a family of battery charger front-end integrated circuits, which dramatically increases protection when charging a cell phone or other portable electronic device. The 2 mm x 2 mm safety circuits protect a system from input over-voltage, over-current and battery over-voltage 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 new 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(TM) 3 product family, allowing the host processor to apply additional corrective actions.
Input Over-Voltage Challenges
Input over-voltage 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 over-voltage threshold of 5.85 V. Another version of the circuit, the bq24316, supports up to 6.8 V.
High-Input Over-Current Protection
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.
Battery Over-Voltage Protection
Potential hazardous events may occur if single-cell, Li-Ion and Li-Polymer batteries are over-charged beyond their float voltage — typically around 4.2 V. 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 over-voltage is detected, interrupts the input charging source.
Key Technical Features of the bq24314 and bq24316:
- Provides protection for three variables: input over-voltage, input over-current and battery over-voltage
- 30-V maximum input voltage
- Integrated power FET and current sensor that supports up to 1.5-A input current
- Less than 1 us response time against input over-voltage
- Input over-voltage protection threshold at 5.85 V (bq24314) or 6.8 V (bq24316)
- High immunity against false triggering due to current transients
- Status indication – fault condition
- Thermal shutdown
Pricing and Availability
The bq24314 and bq24316 are available today in volume from TI and its authorized distributors. Both devices come in a tiny 8-pin, 2 mm x 2 mm small-outline, no-lead (SON) package. Suggested retail pricing for both in 1,000-piece quantities is $0.75. Evaluation modules of the bq24314 and bq24316, design application notes and TI’s easy-to-use online power management selection tool are available.
In the fourth quarter of 2007, 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 10.5 V, the bq24300 devices target low-power applications, like Bluetooth headsets. The bq24300 acts as a linear regulator by managing the output to 5.5 V (or 4.5 V with the bq24304) for voltages up to the input over-voltage threshold. Additionally, a bq24300 circuit can protect against reverse polarity caused by a faulty adaptor using an optional external P-channel MOSFET.