BMS design for pedelec integrates smart cell monitoring IC
ams AG has revealed a reference design that implements controllerless cell monitoring and balancing in the battery management systems (BMS) for a 48V pedelec/e-bike battery, which consists of up to 14 lithium-ion cells.
The design employs two AS8506 smart cell monitoring ICs and few supporting components to monitor the temperature and voltage of up to seven cells each, as well as to implement passive balancing of the cells when charging.
By contrast, conventional BMS designs in pedelecs use dumb voltage monitoring ICs to measure the voltage and temperature of cells, reporting the values to a dedicated battery management microcontroller via a serial communications link. The MCU is required to control safety and protection functions (over- and under-voltage and over-temperature shut-down) and cell balancing.
The ams smart cell monitoring chip, however, includes built-in logic functions for controlling cell safety, protection and balancing. These functions can easily be configured by the user, with the settings saved in an on-board OTP memory.
The chip also features integrated MOSFETs for use in passive cell balancing operations. During charging, each cell's voltage is compared to a user-programmable reference voltage threshold. Up to 100 mA may be discharged through the MOSFET from any cell exceeding the threshold, until all cells have reached the threshold and the battery module is fully charged.
When a chip detects an over- or under-voltage or over-temperature condition, an interrupt signal is transmitted to the pedelec's motor controller IC to complete the required safety shut-down operations.
The design can also be extended to supervise more than 14 cells by daisy-chaining additional AS8506 as required. The smart cell monitoring is in volume production and is priced at $9.10 for 1,000 pieces.
- Paul Buckley
EE Times Europe