在进行测试前，测量TPS74801能准确输出2.5V电压。
为了测试主MCU在一定范围内的电压波动情况下（2.5V ± 10%）是否能正常工作，需要使用外部独立电源为MCU提供2.25-2.75v的波动电压。然后，根据手册将TPS74801的引脚5（EN引脚）连接到GND，使TPS74801（低压差线性稳压器）进入关机模式以使其对MCU的供电没有影响。之后，将外部电源（电压介于2.25和2.75V之间）直接连接到TPS74801的“引脚9和引脚10（输出）”，以测试MCU。
然而在测试结束后，将pin5重新接回高电压时，TPS74801的输出引脚却输出4.2v，该数值不仅是一个异常于2.5V的电压，甚至高于数据手册里所表明的" VOUT Range: 0.8 V to 3.6 V "。
在更换过新的TPS74801元件后，输出引脚仍为4.2V。一个更细节的现象是：测量FB引脚电压，为0V
求助，问题可能出在哪里？
TPS74801: The actual output voltage (4.2 V) is higher than the voltage output range (0.8 V to 3.6 V) indicated in the chip manual
Before testing, tps74801 can accurately output 2.5V voltage.
In order to test whether the master MCU can work normally under the condition of voltage fluctuation within a certain range(2.5V ± 10%), it is necessary to use an external independent power supply to supply the MCU with a fluctuating voltage of 2.25-2.75v. Then, Pin 5 (EN pin) of TPS74801 is connected to GND according to the manual, so that tps74801 (a low-dropout linear regulator)enters shutdown mode and have no effect on power supply to MCU. After that, an external power supply (a voltage between 2.25 and 2.75V) is connected to "pin 9 and pin 10 (out)" of TPS74801 directly to test the MCU.
However, after the test, when pin 5 is connected back to the high voltage, the output pin of tps74801 outputs 4.2V, which is not only an abnormal voltage of 2.5V, but even higher than the "Vout range: 0.8V to 3.6V" indicated in the data manual (TPS748 1.5-A Low-Dropout Linear Regulator With Programmable Soft-Start)
After replacing the old components with the new tps74801, the measured output pin voltage to ground is still 4.2V. A more detailed phenomenon is that the measured FB pin voltage is 0V.
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