Understanding Soft Start of TPS56837
Abstract
Soft start is a common feature used in DC/DC buck converters. Soft start can prevent excessive inrush current and maintain a controlled output voltage during power on. This application note aims to provide a better understanding of TPS56837 soft start. First, this document introduces soft start and covers the general principle of soft start, both internal and external soft start are illustrated. Then, this documents analyzes behaviors related to soft start. Finally, guidance of how to co-lay TPS56837 and TPS56637 is provided.
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1 Why Soft Start is Needed
The soft start function is initiated after EN enable and input voltage reaches UVLO. The soft start circuitry controls the output voltage slope to prevent excessive inrush current, maintain a controlled output voltage, and avoid unwanted voltage overshoots and drops during power management IC start up.
Figure 1-1 shows the difference of output voltage versus time with and without the soft start function. The figure shows that the output voltage overshoots and drops without soft start function. So, soft start is needed for power management IC.
Figure 1-1 Output Voltage With and Without Soft Start Function