Charger chip cuts power supply demands

Combining switch-mode operation with Summit's proprietary Turbo Charge mode the SMB135 dramatically cuts charge time, shrinking or eliminating costly and bulky AC/DC power supplies.

Summit Microelectronics has announced the first product in a family of programmable Li-ion charger ICs aimed at the latest portable consumer applications.

Specially designed to operate with the popular Universal Serial Bus and other current-limited power sources, the SMB135 revolutionises single cell Li-ion and Li-polymer battery charging.

Combining switch-mode operation with Summit's proprietary Turbo Charge mode the SMB135 dramatically cuts charge time, shrinking or eliminating costly and bulky AC/DC power supplies.

Additionally the SMB135 eliminates power cables and connectors by allowing standardisation to a single mechanical connector (USB) for power and data, thereby reducing system cost and complexity.

By addressing the major drawbacks of conventional solutions, namely charge time, power dissipation and solution size, the SMB135 enables new standards for performance, mobility and convenience in portable consumer electronics.

The SMB135 comprises a 1A current-mode step-down (buck) switching battery charger including a fully programmable algorithm for single-cell Li-ion and Li-polymer cells.

All charging parameters - precharge/fast-charge/charge termination current, cell float/precharge voltage, battery temperature/timer safety limits - are configurable via the I2C/SMBus interface enabling a wide variety of algorithms without hardware changes.

The programmable algorithm combined with the inherent current multiplication effect of the switching regulator enables Summit's Turbo Charge mode that delivers up to 750mA charging current from a standard 500mA USB port (up to 1A from an AC/DC adapter).

This represents more than double the charge current typically available from competing solutions, cutting the battery charge time by as much as 66%.

The SMB135 can be programmed either dynamically (real-time using volatile registers), by a microcontroller and software via the I2C/SMBus port, or statically (pre-programmed using nonvolatile registers).

If the static programming mode is used there is no need for software to access the I2C/SMBus interface and the SMB135 functions independently as a customised but parametrically fixed solution.

Additionally the SMB135's switch-mode operation provides another major advantage, reducing power dissipation by as much as 90% compared with competing linear-mode solutions.

This characteristic has a dual benefit - dramatically reduced power dissipation eliminates the need for "thermal current foldback" circuitry of competing linear solutions, which unnecessarily extends charge time.

Also reduced power dissipation allows the SMB135 to be packaged in a tiny 1.3 x 2.1mm chip-scale package - the world's smallest for a battery charger IC.

Linear charger solutions are typically offered in large packages that have high power dissipation capacity and require extra PCB copper "flood" areas for heatsinking.

"Leveraging Summit's field-proven programmable power management technology the SMB135 sets new standards for Li-ion battery charging in portable systems".

"Switch-mode operation and a programmable algorithm enable huge gains in charge time, power dissipation, solution size and safety", stated Abid Hussain, Summit's Director of Marketing.

"The SMB135 is a truly ground-breaking product that will enable a new generation of 'ultra-mobile' devices by simplifying the critical battery charging function".

The SMB135 operates from a +4.35 to +6.0V input making it ideally suited for either USB or AC adapter power sources.

However for applications where the AC adapter may be poorly regulated and/or an aftermarket product the SMB135 will tolerate +10V inputs without damage.

Switching frequency is programmable between 750kHz and 1.25MHz providing for small external passive component size and cost.

Ensuring long battery life when not connected to a DC power source, the reverse leakage current is less than 2uA.

Also when not using the I2C/SMBus port for charge control/monitoring the SMB135 provides a 500/100mA control pin for USB compliance and a status output to drive an LED.

Enhancing reliability the SMB135 integrates overvoltage, short-circuit and thermal protection circuits.

Also the SMB135 protects the battery pack with a programmable battery temperature monitor and charge timers to prevent dangerous charging conditions.

Furthermore, to protect deeply discharged cells, the SMB135 has a 3mA "trickle charge" mode below 2.0V.

This mode allows safe, controlled recovery of the deeply discharged cell until it can accept normal charging currents.

Finally the SMB135's programmability enables future battery upgrades while preserving safety.

For example as newer battery packs employ cell float voltages other than 4.1 or 4.2V, conventional, nonprogrammable charger ICs, at best, can disable charging - the worst case could be a battery pack fire or explosion.

However with the SMB135, as long the new battery pack can be properly identified, the charging algorithm is dynamically adapted (up to 4.62V) and it continues to safely charge the battery.

The SMB135 is well suited to handheld consumer electronics devices such as 2.5G/3G phones, PDAs/smartphones, Bluetooth headsets, portable media players (PMP), portable game consoles, digital still cameras (DSC)/camcorders (DCC) and GPS terminals.

In particular it is the ideal battery charging solution for applications that use a single USB connector to provide both data and power.

The SMB135 has an operating temperature range of 0 to +70C and is available in the 1.3 x 2.1mm 15-ball chip-scale (CSP) package that is lead-free and RoHS-standards compliant.

Available now in production quantities, the device is priced at $0.98 each in quantities of 10,000 units.

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