TPS54341_15 datasheet(16/48 Pages) TI

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TPS54160

SS/TR

PWRGD

TPS54160

SS/TR

PWRGD

TPS54341

SS /TR

TPS54341

PWRGD

SS /TR

PWRGD

TPS54341

SLVSC61 – NOVEMBER 2013

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DETAILED DESCRIPTION (continued)

Sequencing

Many of the common power-supply sequencing methods are implemented using the SS/TR, EN, and PWRGD

pins. The sequential method is implemented using an open-drain output of a power-on reset pin of another

device. The sequential method is illustrated in Figure 29 using two TPS54341 devices. The power good is

connected to the EN pin on the TPS54341 device which enables the second power supply once the primary

supply reaches regulation. If needed, a 1-nF ceramic capacitor on the EN pin of the second power supply

provides a 1-ms startup delay. Figure 30 shows the results of Figure 29.

Figure 29. Schematic for Sequential Startup

Figure 30. Sequential Startup Using EN and

Sequence

PWRGD

Figure 31. Schematic for Ratiometric Startup

Figure 32. Ratiometric Startup Using Coupled

Sequence

SS/TR pins

Figure 31 shows a method for ratiometric start-up sequence by connecting the SS/TR pins together. The

regulator outputs ramp up and reach regulation at the same time. When calculating the soft-start time the pullup

current source must be doubled in Equation 5. Figure 32 shows the results of Figure 31.

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