Datasheet

SS /TR
TPS54060
EN
PWRGD
SS /TR
EN
PWRGD
EN1
PWRGD1
VOUT1
VOUT2
EN1,EN2
VOUT1
VOUT2
EN
TPS54160
3
SS/TR
4
PWRGD
6
EN
TPS54160
3
SS/TR4
PWRGD
6
TPS54060
TPS54060
TPS54060
SLVS919A –JANUARY 2009–REVISED JULY 2010 www.ti.com
DETAILED DESCRIPTION (continued)
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 output of a power on reset pin of another
device. The sequential method is illustrated in Figure 31 using two TPS54060 devices. The power good is
coupled to the EN pin on the TPS54060 which will enable the second power supply once the primary supply
reaches regulation. If needed, a 1nF ceramic capacitor on the EN pin of the second power supply will provide a
1ms start up delay. Figure 32 shows the results of Figure 31.
Figure 31. Schematic for Sequential Start-Up Figure 32. Sequential Startup using EN and
Sequence PWRGD
Figure 33. Schematic for Ratiometric Start-Up Figure 34. Ratio-Metric Startup using Coupled
Sequence SS/TR pins
Figure 33 shows a method for ratio-metric start up sequence by connecting the SS/TR pins together. The
regulator outputs will 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 6. Figure 34 shows the results of Figure 33.
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