外接时钟给CLK管脚，是不是为了同步TPS84259的开关频率，避免开关噪声影响其他信号？还有其他用途吗？
另外CLK的电压范围是多少呢？根据手册12.10节，"The clock signal amplitude must transition lower than 0.5 V and higher than 2.2 V."
同时4.4节CLK High-Level Threshold和Low-Level Threshold “with respect to A_VOUT”
This voltage rating is referenced to A_VOUT, not GND.
A_VOUT和VOUT短接（-8V），CLK要参考AVOUT吗？CLK范围是-5.8V？
