TPS51120在低负载状态下（light load condition）会自动降低开关频率来维持高效率。请参考数据手册低13页，关于Light Load Operation的描述： TPS51120 automatically reduces switching frequency at light load condition to maintain high efficiency. This reduction of frequency is achieved smoothly and without an increase in load regulation. Detail operation is described as follows. As the output current decreases from heavy load condition, the inductor current is also reduced and eventually comes to the point that its ‘valley’ touches zero current, which is the boundary between continuous conduction and discontinuous conduction modes. The rectifying MOSFET is turned off when this zero inductor current is detected. The on-time is kept the same as that in the heavy load condition. As the load current further decreases, the converter runs in discontinuous conduction mode and it takes longer and longer to discharge the output capacitor to the level that requires next ‘ON’ cycle. This results in reducing the switching frequency. In reverse, when the output current increases from light load to heavy load, switching frequency increases to the constant predetermined frequency as the inductor current reaches to the continuous conduction. The transition load point to the light load operation IOUT(LL) (i.e. the threshold between continuous and discontinuous conduction mode) can be calculated as shown in Equation 1. where f is the PWM switching frequency which is determined by TONSEL pin. Switching frequency versus output current in the light load condition is a function of L, f, VIN and VOUT, but it decreases almost proportional to the output current from the IOUT(LL) given in Equation 1. 如果能提供更精确的波形更有助分析。如有必要，请通过下面的Email联系德州仪器产品信息中心技术获取技术支持： ti-china@ti.com
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