Datasheet

Vo u t 2

Vo u t 1

P W R GD 1

E N 2

EN1

SS/TR2

TPS54519

EN2

PWRGD2

SS/TR1

EN1

PWRGD1

TPS54519

Tss(mS) Iss( A)

Css(nF) =

Vref(V)

´ m

TPS54519

www.ti.com

SLVSAT3A –SEPTEMBER 2011–REVISED DECEMBER 2013

SLOW START / TRACKING PIN

The TPS54519 regulates to the lower of the SS/TR pin and the internal reference voltage. A capacitor on the

SS/TR pin to ground implements a slow start time. The TPS54519 has an internal pull-up current source of

2.4μA which charges the external slow start capacitor. Equation 4 calculates the required slow start capacitor

value where Tss is the desired slow start time in ms, Iss is the internal slow start charging current of 2.4 μA, and

Vref is the internal voltage reference of 0.6 V.

(4)

If during normal operation, the VIN goes below the UVLO, EN pin pulled below 1.18 V, or a thermal shutdown

event occurs, the TPS54519 stops switching and the SS/TR is discharged to 0 volts before reinitiating a

powering up sequence.

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 18 shows the sequential method. The power good is coupled to the EN pin on the

TPS54519 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 20.

Figure 18. Sequential Start-Up Sequence Figure 19. Sequential Startup using EN and

PWRGD

Product Folder Links: TPS54519