March 18, 2014 – ams AG (SIX: AMS, Country Manager Jong-Deok Lee), a specialist in high-performance analog ICs and sensors, announced a reference design targeting lithium-ion batteries for pedelecs/e-bikes. This reference design enables accurate cell monitoring and balancing functions in the battery management system (BMS) without using a microcontroller.

With the newly announced design, battery pack and electric bicycle manufacturers will be able to realize a more valuable bill of materials (BoM) compared to currently commercialized batteries, thereby benefiting from cost reduction and simpler circuit design.

This reference design from ams is suitable for 48V electric bicycle batteries that can be configured with up to 14 lithium-ion cells. This reference design uses two AS8506 smart cell monitoring ICs with a small amount of support components, each IC monitoring the temperature and voltage of up to seven cells individually and implementing passive balancing of the cells during charging.

In contrast, conventional BMS designs used in electric bicycles utilize dumb voltage monitoring ICs to measure cell voltage and temperature, and report these values to a dedicated battery management microcontroller (MCU) via a serial communication link. The MCU used in this case is necessary to manage safety and protection functions for overvoltage, undervoltage, and overheating shutdowns, as well as to control cell balancing.

However, ams’s AS8506 has built-in logic functions to control the cell’s safety, protection, and balancing processes. These functions are provided with configuration settings stored in the onboard OTP memory, allowing the user to easily configure them. This device incorporates a highly integrated MOSFET for use in passive cell balancing operations. During charging, the voltage of each cell is compared to a user-programmable reference voltage threshold. Up to 100mA can be discharged through the MOSFET from each cell exceeding the threshold until all cells reach the threshold and the battery module is fully charged.

This architecture, which operates battery monitoring and cell balancing, is implemented within the AS8506 voltage monitoring device and does not require a dedicated MCU, which is required in conventional electric bicycle battery designs. The moment the AS8506 detects overvoltage, undervoltage, or overheating conditions, it transmits an interrupt signal to the motor controller IC so that the required safe shutdown can be completed.

Bernd Gessner, Vice President and General Manager of the Automotive Business Unit at ams, stated, “Battery life, safety, and operating time have a tremendous impact on consumers when choosing an electric bicycle. Through ams’ controller-free reference design, electric bicycle manufacturers can meet consumer demands by providing superior safety and battery performance, while utilizing a simpler and more cost-effective architecture compared to existing commercial products.”

The reference design can be used in any electric bicycle battery using up to 14 lithium-ion cells. This design can expand and supervise more than 14 cells by daisy-chaining additional AS8506 ICs as needed.

Reference design files are available via ams upon request.