One single BQ769x2 family battery monitor can support up to a 16s battery pack which is good enough for 36-V and 48-V applications. For 60 V and higher battery packs, two stacked BQ769x2 family monitors are required. This document describes how to stack devices for the BQ769x2 monitor family and utilize the integrated charge pump to drive high-side N-channel MOSFETs. The key design considerations are analyzed to secure fast and robust MOSFET switching on and off times, minimize the current gaps between two stacked groups, and enable easy communications design between the stacked BQ769x2 devices and host MCU.
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Because of the weight limit and longer endurance needs, the battery cell chemistry of the e-motorcycle, light electric vehicles, and garden tool battery packs is shifting from Lead-acid to Li-ion, Li-polymer, or Li-ion phosphate (LiFePO4) types and the pack voltage is shifting from 36 V or 48 V to 60 V or 72 V, or even higher. For 60 V and higher battery packs, two stacked BQ769x2 family monitors are required.
One critical requirement of a battery pack is how to attain safe use during the entire battery pack lifetime. The stacked BQ769x2 family monitor architecture spawns some challenges of how to monitor the information of all battery cells and detect unsafe working conditions, and how to control the on and off switches to protect the battery pack away from dangerous use-cases. TI released the TIDA-010247 reference design where a stacked BQ769x2 family monitors a battery-pack design with high-side N-MOSFET control. #FIG_TG5_XXH_VVB shows the TIDA-010247 block diagram. This document identifies the common design challenges in stacked BQ769x2 family monitor architecture and explains how to address the challenges.
To cover battery packs with higher than 16s cells, and greater than 60-V applications, two BQ769x2 family monitors are stacked to monitor up to 32s battery cells. Each BQ769x2 monitors up to 16s battery cells in one group. The bottom BQ769x2 shares the same ground with the whole pack and MCU, while the top BQ769x2 references the stack voltage of the bottom group. Therefore, an isolation device or a high-voltage level shifter is required for the communications between the top BQ769x2 and the MCU.