Datasheet

SS/TR1
TPS54618
EN1
PWRGD1
SS/TR2
TPS54618
EN2
PWRGD2
EN
SS
VO1
VO2
EN1
EN2
VO1
VO2
SS2
TPS54618
EN2
PWRGD2
SS1
EN1
PWRGD1
TPS54618
SLVSAE9D –NOVEMBER 2010–REVISED DECEMBER 2013 www.ti.com
SEQUENCING
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 27 shows the sequential method. The power good is coupled to the EN pin on the
TPS54618 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 29.
Figure 27. Sequential Start-Up Sequence Figure 28. Sequential Startup using EN and
PWRGD
Figure 29. Schematic for Ratio-metric Start-Up Figure 30. Ratio-metric Startup
Sequence
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