Datasheet

SS/TR
EN
PWRGD
SS/TR
EN
PWRGD
TPS54320
TPS54320
PWRGD = 2 V / div
EN = 2 V / div
Vout1 = 1 V / div
Vout2 = 1 v / div
Time = 2 msec / div
Time = 2 msec / div
EN = 2 V / div
Vout1 = 1 V / div
Vout2 = 1 V / div
SS/TR
TPS54320
EN
PWRGD
SS/TR
EN
PWRGD
TPS54320
TPS54320
www.ti.com SLVS982A –AUGUST 2010–REVISED SEPTEMBER 2010
Sequencing (SS/TR)
Many of the common power supply sequencing methods can be implemented using the SS/TR, EN, and
PWRGD pins.
The sequential method is illustrated in Figure 22 using two TPS54320 devices. The power good of the first
device is coupled to the EN pin of the second device which enables the second power supply once the primary
supply reaches regulation. Figure 23 shows the results of Figure 22.
Figure 22. Sequential Start Up Sequence
Figure 23. Sequential Start Up using EN and
PWRGD
Figure 24 shows the method implementing ratio-metric sequencing by connecting the SS/TR pins of two devices
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 5. Figure 25 shows the results of Figure 24.
Figure 25. Ratio-metric Startup using Coupled
SS/TR Pins
Figure 24. Ratiometric Start Up Sequence
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