JAJSBF8B June 2011 – April 2018 TPS54478
PRODUCTION DATA.
Many of the common power supply sequencing methods can be implemented using the SS/TR, EN, and PWRGD pins. The sequential method can be implemented using an open drain or collector output of a power on reset pin of another device. Figure 23 shows the sequential method. The PWRGD is coupled to the EN pin on the TPS54478 which enables the second power supply once the primary supply reaches regulation.
Ratio-metric start up can be accomplished by connecting the SS/TR pins together. The regulator outputs ramp up and reach regulation at the same time. When calculating the slow start time the pull up current source must be doubled in Equation 4. The ratio metric method is illustrated in Figure 25.