USB battery charger for Li-Ion/Li-Polymer powered systems

January 23rd, 2009 • Related • Filed Under

Summit Microelectronics has introduced its third-generation programmable battery charger integrated circuit (IC) for single-cell Li-Ion and Li-Polymer powered systems. The SMB339 is a programmable single-cell lithium-ion/lithium-polymer battery charger designed for a variety of portable applications. The device provides a simple and efficient way to charge high-capacity Li-Ion batteries via a USB or AC adapter input. Furthermore, the SMB339 is able to automatically adjust input current level by detecting the AC/DC adapter’s maximum stable output current, thereby automatically matching wall adapter to electronic device. The SMB339 is ideal for a wide range of portable devices such as mobile phones, smartphones/PDAs, portable media/MP3 players (PMP), portable GPS navigation, portable game consoles, and digital cameras/camcorders (DSC/DCC).

USB battery charger

The battery charger is industry’s first solution that allows true universal USB and AC/DC battery charging. First, the Automatic Power Source Detection differentiates between a USB 2.0 port and a “USB” AC/DC adapter. This allows the charger to comply with the USB 2.0 100/500mA limits, but also to draw higher current levels from an AC/DC wall adapter. Subsequently, since AC/DC adapters can vary widely in current rating, Automatic Input Current Limit (patent pending) detects the maximum current capability of the AC/DC adapter (can be as low as 300mA for Chinese chargers to more than 1.5A per USB charging specification) and automatically programs the SMB339’s input current limit accordingly. Unlike existing solutions, the battery charger performs these functions independently, without the need for external components or system software operation. These two features ensure true USB compliance while providing the fastest safe charging from any source (including AC/DC adapters), giving end-users the best charging performance in any situation. The resulting improved user experience translates into fewer service calls, fewer merchandise returns and increased subscriber revenue for wireless carriers.

The features and integration of the SMB339 make it especially suited for devices that include a USB interface because it allows a tiny, low-cost industry-standard micro USB connector to be the primary data and power/charging interface. The SMB339 integrates the largest feature set in the industry, including compatibility with all relevant industry standards: USB 2.0 Specification, USB “On-The-Go” Supplement, USB Battery Charging Specification 1.0, IEEE1725 Standard, Chinese USB Charging Specification, and others.

The SMB339 can switch between USB mode and AC Adapter mode and works seamlessly in conjunction with a USB controller. The SMB339 offers the option to automatically differentiate an AC/DC wall adapter from a USB2.0 hub via the D+/D- USB lines, making it compatible with USB battery charging specification 1.0. This innovative charging solution automatically adapts to and delivers the fastest battery charging from any power source (USB host/hub, AC/DC, etc.) without the software required in typical implementations. Additionally, high integration reduces bill-of-material count/cost and solution size to levels comparable to inferior linear charging solutions, while cutting power dissipation by 80percent. Like all Summit’s solutions, digital programmability is built-in, providing design and system flexibility at no additional cost.

The SMB339, based on a high performance 3MHz switch-mode architecture, is the industry’s most integrated single-cell Li-Ion charger. The device’s high-efficiency operation, coupled with Summit’s proprietary TurboChargeTM patent-pending technology, allows for highest charging current (up to 750mA from 500mA USB source) and lowest power dissipation. This allows for slim industrial designs and significantly faster charging times; two valuable differentiating factors for handset and other consumer products. Unlike conventional devices, the SMB339’s high-efficiency, switchmode operation eliminates the thermal problems of conventional linear solutions. Also the buck converter architecture effectively multiplies the input current to increase charge rate for the Li+ cell and uses current limited supplies like USB more efficiently. The SMB339 also supports USB On-the-Go devices by providing the required USB-OTG +5V power supply using the Li-Ion battery as a source.

Like its predecessor, the SMB339 is also capable of providing USB On-The-Go (OTG) power support, without the need for additional external components. The device has the ability to reverse its power path when not charging, thereby supplying 5V and up to 500mA to VBUS, exceeding the USB OTG Supplement Specification. The chip’s parameters are programmable in non-volatile and volatile memory for power-up configuration and in-system adjustments via the I2C host interface. This provides maximum design flexibility to address a variety of system and battery designs and allows the implementation of sophisticated embedded charging algorithms. The SMB339 operates with an input range from +3.5V to +6.2V input and safely withstands continuous input over-voltage up to +16V (non-operating), while protecting downstream circuitry. The SMB339 is offered in a tiny 2.3mm x 2.0mm, 20-ball, lead-free chip-scale (CSP) package with an operating temperature range of –30C to +85C.

Charge control includes qualification, trickle-charge, pre-charge, constant current/constant voltage, float voltage and termination/safety settings that are fully programmable via a serial I2C/SMBus, making the device truly a flexible solution. Fast charge current level can be set via I2C (limited in USB mode to ensure 100mA or 500mA input). Builtin is reverse-current blocking to prevent inadvertent cell discharge. The SMB339 offers the option to automatically charge the battery only when the battery voltage is below a selectable “dead-battery” threshold. High-frequency operation and integrated power FETs contribute to a reduced external component count and size.

A wide variety of programmable safety features are also integrated to meet the strictest safety standards, including IEEE1725. These include dual redundant protection for input/output current and voltage, chip and battery thermal protection, hardware and software safety timers, battery missing detection and a variety of status and fault registers. The SMB339 also offers several features that protect the battery pack as well as the charger and input circuitry: over-current, under/overvoltage and thermal protection. Ultra-accurate, 1% battery float voltage control improves battery capacity utilization. The STAT output is an interrupt to flag various status/flag events (programmable selection) and the status register can be read via the serial port. The battery charger is available in an ultra-compact lead-free uCSP-20 and in a 4×4 QFN-24 package and is rated over the –30C to +85C temperature range.

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