Power Sources

48-V Li-ion Battery Pack Reference Design with High-Accuracy SOC Gauging

The TIDA-010030 reference design from Texas Instruments is a low standby and ship mode current consumption and high SOC gauging accuracy 13S, 48-V Li-ion battery pack design. It monitors each cell voltage, pack current and temperature with high accuracy and protects the Li-ion battery pack against overvoltage, undervoltage, over temperature and over current situations. The SOC gauging, based on bq34z100-g1, takes advantage of an impedance tracking algorithm and achieves as high as 2% accuracy at room temperature.

Through a well-designed auxiliary power supply strategy and high efficiency, low quiescent current dc-dc converter LM5164, this design achieves 50-µA stand-by and 5-µA ship mode consumption, saving more energy and allowing longer shipping time and idle time.

Also, this design supports a well running firmware, which helps to decrease product research time. Features include:

  • 2% battery pack SOC accuracy at room temperature
  • 50-µA current consumption when in standby mode
  • 15-µA current consumption when in shipping mode
  • Robust and programmable protection, including: cell over voltage, cell under voltage, overcurrent discharge, short circuit, overtemperature and undertemperature
  • Support 100-mA cell balancing
  • High-side charging and discharging MOSFETs and support pre-discharge function
System Description and Design Philosophy

TIDA-010030 reference design board

The e-bike market is growing rapidly. Because of the weight limited and longer endurance request, the battery cell chemistries of the battery pack is shifting to Li-ion, Li-polymer, or Li-iron phosphate types. These chemistries are good in both volumetric and gravimetric energy density.

While these chemistries provide high energy density and thereby lower volume and weight as an advantage, they are associated with safety concerns and need more complicated monitoring and accuracy capacity gauging. Those concerns are undervoltage (UV) and overvoltage (OV), over temperature (OT), and overcurrent (OC), over discharge and charge current, all which contribute to the accelerating cell degradation and may lead to thermal runaway and explosion.

Therefore, the pack current, temperature and each cell voltages should be timely monitored in case of some unusual situations. And pack must be protected against all these situations.

The capacity gauging is able to calculate how much capacity is still stored in the pack and predict the run-time and charge time, avoiding suddenly shutdown when ridding the ebike. A good accuracy gauging design can also extend run-time because it allows users using all available battery capacity without damaging the battery cells. Another important feature is the current consumption when the e-bike is in ship mode or idle.

TIDA-010030 reference design block diagram (click on block diagram to enlarge)

This design is mainly focus on e-bike battery pack applications and also suitable for other high cell applications, such as e-scooter battery pack, mowing robot battery pack, etc. It contains both primary and secondary protection to ensure safety use of the battery pack.

The primary protection will protect the battery pack against all unusual situations, including: over voltage, under voltage, over discharge current, short circuit, over temperature and under temperature.

The secondary protection which uses hardware over voltage protection is an add on board with is easily remove and added based on actual demands. This design utilizes Impedance Track™ gauging algorithm which helps to achieve very high SOC gauging accuracy even for old battery cells or at low or high temperature.

This implementation carefully designs the auxiliary power and firmware, which achieves quite low ship mode and standby mode current consumption (5-µA for ship mode and 50-µA for standby mode). Also, this design supports a well running firmware based on a low power consumption MSP430TM MCU MSP430FR2155.

Texas Instruments Incorporated
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