Datasheet

> ´ - ´ DR1 2800 Vout1 180 V

V = Vout1 Vout2D -

D -

Vref R1

R2 =

Vout2 + V Vref

Vout2 + V Vssoffset

R1 =

Vref Iss

SS/TR

TPS54622

PWRGD

SS/TR

PWRGD

TPS54622

www.ti.com

SLVSA70B –MARCH 2011–REVISED JANUARY 2014

Figure 23 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 23. Ratiometric Start Up Sequence

Ratio-metric and simultaneous power supply sequencing can be implemented by connecting the resistor network

of R1 and R2 shown in Figure 24 to the output of the power supply that needs to be tracked or another voltage

reference source. Using Equation 6 and Equation 7, the tracking resistors can be calculated to initiate the Vout2

slightly before, after or at the same time as Vout1. Equation 8 is the voltage difference between Vout1 and

Vout2.

To design a ratio-metric start up in which the Vout2 voltage is slightly greater than the Vout1 voltage when Vout2

reaches regulation, use a negative number in Equation 6 and Equation 7 for deltaV. Equation 8 results in a

positive number for applications where the Vout2 is slightly lower than Vout1 when Vout2 regulation is

achieved. .

The deltaV variable is zero volt for simultaneous sequencing. To minimize the effect of the inherent SS/TR to

VSENSE offset (Vssoffset, 29mV) in the slow start circuit and the offset created by the pull-up current source

(Iss, 2.3μA) and tracking resistors, the Vssoffset and Iss are included as variables in the equations.

To ensure proper operation of the device, the calculated R1 value from Equation 6 must be greater than the

value calculated in Equation 9.

(6)

(7)

(8)

(9)

Product Folder Links :TPS54622