Summit Microelectronics has announced the first product in a family of Programmable Li-Ion Charger IC's. It was specially designed to operate with the Universal Serial Bus and other current-limited power sources for single cell Li-Ion and Li-Polymer battery charging. The SMB135 eliminates power cables and connectors by allowing standardization to a single mechanical connector (USB) for power and data.

Features

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 - pre-charge/fast-charge/charge termination current, cell float/pre-charge 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). 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 non-volatile 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 customized but parametrically fixed solution.

Additionally the SMB135's switch-mode operation reduces power dissipation by as much as 90% compared to other linear-mode solutions. This characteristic has a dual benefit - 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 1.3mm x 2.1mm chip-scale package. The SMB135 operates from a +4.35V to +6.0V input making it 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 2 microampere. Also when not using the I2C/SMBus port for charge control/monitoring the SMB135 provides a 500mA/100mA control pin for USB compliance and a STATUS output to drive an LED. Enhancing reliability the SMB135 integrates over-voltage, 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. F

inally the SMB135's programmability enables future battery upgrades while preserving safety. For example as newer battery packs employ cell float voltages other than 4.1V or 4.2V a conventional, non-programmable charger IC's, 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.

Applications

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.

Pricing and Availability

The SMB135 has an operating temperature range of 0 degrees C to +70 degrees C and is available in the 1.3mm x 2.1mm 15-ball chip-scale (CSPT) 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.

Design Software and Programmer for Prototype Development

To speed user product development, Summit offers customers the SMB135EV companion evaluation board and a graphical user interface (GUI) software. This is a development tool that lets designers manipulate the characteristics of their systems. The SMB135EV design kit includes menu-driven Microsoft Windows GUI software to automate programming tasks and also includes all necessary hardware to interface to the parallel or USB port of a laptop or PC. Once a user completes design and prototyping, the SMB135EV automatically generates a HEX data file that can be transmitted to Summit for review and approval. Summit then assigns a unique customer identification code to the HEX file and programs the customer's production devices prior to final electrical test operations. The design kit software can be downloaded today from Summit's website.