USB 电缆的长度会对电流产生影响，但这主要是由于电缆的电阻造成的。下面是其工作原理：
1. 电缆电阻： USB 电缆越长，电阻越大。这种电阻会导致电缆上的电压下降，从而影响设备端的可用电压水平。
2. 电压下降：如果由于电缆电阻导致电压下降过多，设备可能会消耗更多的电流来补偿较低的电压，以维持其运行，从而可能导致其超过 USB 挂起模式规定的电流限制。
不过，当设备处于 USB 挂起模式时，其设计旨在最大限度地降低功耗，通常电流小于 2.5mA。由于电流消耗非常低，电缆的电阻也就不那么重要了，因此电缆上的压降也会很小。
总之： 在 USB 挂起模式下，电流消耗非常低，电缆长度对电流的影响通常可以忽略不计。关键因素是确保设备本身的设计能满足 USB 挂起模式的低功耗要求，而与电缆长度无关。
| the length of the USB cable can have an impact on the current, but it is primarily due to the resistance of the cable. Here’s how it works: 1. Cable Resistance: The longer the USB cable, the higher the resistance. This resistance can cause a voltage drop along the cable, which may affect the voltage level available at the device end. 2. Voltage Drop: If the voltage drops too much due to the cable resistance, the device might draw more current to compensate for the lower voltage in order to maintain its operation, potentially causing it to exceed the current limits specified for USB suspend mode. However, when a device is in USB suspend mode, it is designed to minimize power consumption, typically drawing less than 2.5mA. The resistance of the cable becomes less significant because the current draw is very low, and thus the voltage drop across the cable will also be minimal. In summary: For USB suspend mode, where the current draw is very low, the impact of the cable length on the current is generally negligible. The key factor is ensuring that the device itself is designed to meet the low power requirements of the USB suspend mode, regardless of the cable length. |
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