TPS54260
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SLVSA86 –MARCH 2010
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 30 using two TPS54260 devices. The power good is
coupled to the EN pin on the TPS54260 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 31 shows the results of Figure 30.
TPS54260
PWRGD
EN
EN
EN1
SS/TR
SS /TR
PWRGD1
PWRGD
VOUT1
VOUT2
Figure 30. Schematic for Sequential Start-Up
Sequence
Figure 31. Sequential Startup using EN and
PWRGD
TTPPSS554412660
3
4
6
EN
EN1, EN2
SS/TR
PWRGD
VOUT1
TPS54260
TPS54160
VOUT2
3
4
6
EN
SS/TR
PWRGD
Figure 32. Schematic for Ratiometric Start-Up
Sequence
Figure 33. Ratio-Metric Startup using Coupled
SS/TR pins
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