Datasheet

Time = 2 msec / div
EN = 2 V / div
Vout1 = 1 V / div
Vout2 = 1 V / div
SS/TR
TPS54521
EN
PWRGD
SS/TR
TPS54521
EN
PWRGD
VOUT1
VOUT 2
R1
R2
R3
R4
> ´ - ´ DR1 2800 Vout1 180 V
V = Vout1 Vout 2D -
´
D -
Vref R1
R2 =
Vout2 + V Vref
D
´
Vout2 + V Vssoffset
R1 =
Vref Iss
TPS54521
www.ti.com SLVS981C –JUNE 2010–REVISED AUGUST 2013
The deltaV variable is zero volts 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. Figure 29
shows the result when deltaV = 0V.
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)
Figure 26. Ratiometric and Simultaneous Startup Sequence
Figure 27. Ratio-metric Startup with Vout1 Leading Vout2
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