Battery management chip targets e-bikes and HEVs

December 04, 2013 // By Christoph Hammerschmidt
Highly accurate charge/discharge control along with monitoring and protection functions for Li-ion secondary battery packs are the main features of Rohm Semiconductors' new battery management ICs for smaller batteries typically used in electric bicycles.

These rechargeable battery packs are used in E-Bikes, Power Tools, UPS (Uninterruptible Power Supplies) and HEV applications which experience rapid growth over the next few years. Li-ion batteries have proven to be an efficient high performance power source; however, safety functions such as voltage monitoring, over-charge / over-discharge detection, cell balancing and temperate measurement play a crucial role in order to secure stable and safe operation.

The ML5218 is a Li-ion battery monitoring IC for packs of 5 to 16 cells detecting overcharge or over-discharge as well as overcurrent of each cell. This makes the device adaptable to systems using safer lithium iron phosphate batteries of multiple cells connected in series. The operating current consumption is similar to that of the conventional models. The current consumption in the power-down mode is minimized to around zero, and the load on the battery pack during long-term storage has been reduced significantly as well. Also, the built-in 100mA cell-balancing switch eliminates the need of an external circuit for cell balancing, facilitating a low-cost system design. The battery remaining charge display function can be configured using up to five external LEDs. Monitoring of temperatures for up to eight locations is implemented by connecting thermistors in order to add to system safety. The ICs also integrate the Gate driver for an automatic ON/OFF control of the external N-ch FET for the charge and discharge.

For a complete protection solution, Rohm offers the external MCU ML610Q486P which can be used in combination with the ML5238. The MCU is an 8bit high-performance controller based on the low power Microcontroller series ML610Q4xx with integrated Flash memory to store the register settings. The monitoring IC can provide the 3.3V power supply to the MCU so that no external voltage regulator is needed. Based on the results of the voltage control of each cell or the entire battery pack, as well as the monitoring of the charge and discharge current,