Research on Low Leakage Current Voltage Sampling Method for Multi-cell Series Battery Packs
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摘要: 针对多节串联电池组采样电路存在通道漏电流导致各节电池电压不一致和影响采样精度的问题，该文提出一种应用于14节串联锂电池的低漏电流电池电压采样方法。通过分析漏电流的产生机制，采用运放隔离有源驱动技术，减小各节电池的通道漏电流，同时为了减小高压MOSFET带来的面积开销，改进了高压域运算放大器。基于0.35 μm高压BCD(Bipolar CMOS DMOS)工艺对电路进行了详细设计和完整性能验证，结果表明，所设计的电池电压采样电路版图面积仅为3.105×0.638 mm2，在不同的温度和工艺角组合下，最大通道漏电流低至48.9 pA。在全面的PVT(Process Voltage Temperature)验证下，电池电压采样最大测量误差小于1.25 mV。该方法将采样过程对电池电压不一致性的影响从18.56%降低至2.122 ppm，为高可靠高精度多节串联电池管理系统提供了有效的解决方案。Abstract:
Objective The battery voltage sampling circuit is a key component of the Battery Management Integrated Circuit (BMIC). It performs real-time monitoring of cell voltages, and its performance directly affects the safety of series battery packs. Traditional resistive voltage sampling circuits exhibit channel leakage current, which affects cell-voltage consistency and sampling accuracy. In addition, the level-shifting circuit in the high-voltage domain contains high-voltage operational amplifiers, and the use of many high-voltage MOSFETs increases area overhead. Methods This study proposes a low-leakage-current battery voltage sampling circuit for 14-series lithium batteries. Based on the traditional resistive sampling structure, channel leakage current is reduced to the pA level by designing an operational-amplifier-isolated active-drive technique. Voltage conversion methods are selected according to the voltage domain of each cell group. The first section of the battery uses a unity-gain buffer for isolation and then performs voltage conversion through resistive division. Sections 2 to 13 use operational-amplifier-isolated active driving to follow each cell voltage synchronously, after which the followed voltage is converted to a ground-referenced level through a level-shifting circuit. The voltage sampling process of the highest-section battery draws power from the entire battery stack and does not affect pack consistency; therefore, this section directly adopts the level-shifting circuit for voltage conversion. Results and Discussions The circuit was designed and verified using a 0.35 µm high-voltage BCD process. The overall layout area of the proposed sampling circuit is 3 105 µm × 638 µm (Fig. 10). Verification results show that, across different process corners and temperatures, the maximum channel leakage current after applying the isolated active-drive technique is only 48.9 pA. In contrast, the minimum leakage current of the traditional sampling circuit is 1.169 × 106 pA (Fig. 12, Fig. 13). The effect of the sampling process on cell-voltage inconsistency is reduced from 18.56% to 2.122 ppm (Fig. 14). Under full PVT verification, the maximum measurement error of the proposed sampling circuit is 0.9 mV (Fig. 15, Fig. 16, Fig. 17). Conclusions This study proposes an operational-amplifier-isolated active-drive technique to address the channel leakage issue in traditional resistive voltage sampling circuits, which affects cell-voltage consistency and measurement accuracy. Using the proposed circuit, the maximum channel leakage current is 48.9 pA, the cell-voltage inconsistency is 2.122 ppm, and the maximum measurement error is 1.25 mV. The circuit achieves very low leakage current while maintaining sampling accuracy. The proposed low-leakage-current sampling circuit is suitable for 14-series lithium battery management chips. -
表 1 参数对比
文献[18] 文献[20] 文献[21] 文献[22] 文献[23] 文献[25] 本文 工艺(µm) 0.18 0.18 0.18 0.18 0.18 — 0.35 电池节数 16 4~7 3 17 7 16 14 通道漏电流补偿 — 电流镜
钳位反馈型电流镜
钳位反馈型运算放大器
钳位反馈型运算放大器
钳位反馈型— 运放隔离
有源驱动型最大通道漏电流 16.25 μA 58 nA 20.34 nA 30 nA 30 nA — 48.9 pA 最大测量误差(mV) ±0.21 — — ±2 ±1.92 ±2.8 ±1.25 版图面积(mm2) 3.245×3.112 0.95×0.82 — 2.92×3.23 — — 3.105×0.638 数据类型 S T T T S T S *T表示数据类型为测试数据，S表示数据类型为仿真数据 
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