如果流经低侧 MOSFET 的电流超过 ILIMIT 电流,电流限制电路将激活。在电机启动、高扭矩事件或失速情况下可能会产生大电流。限流电路在三相的低侧功率 FET 上使用内部检测 FET。图 7-22 展示了电流限制电路的实现方式。ILIM 引脚通过将 RLIMIT 从 ILIM 连接到 AGND 来设置 ILIMIT。方程式 3 会计算目标 ILIMIT 阈值所需的电阻值,单位为欧姆。
方程式 3. RLIMIT = 9000/ILIMIT
当电流限制激活时,高侧 FET 将禁用,直到下一个 PWM 周期开始,如图 7-23 所示。通过配置 SPI 器件型号中的 ILIM_RECIR 位,低侧 FET 可以在制动模式或滑行(高阻态)模式下运行。在硬件器件中,当限流触发时,该器件在制动模式下运行。
当电流限制在同步整流模式下激活时,电流通过低侧 FET 再循环,而高侧 FET 被禁用,如图 7-24 所示。当电流限制在异步整流模式下激活时,电流通过低侧 FET 的体二极管再循环,而高侧 FET 被禁用,如图 7-25 所示。
图 7-24 制动状态
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