Datasheet

SS/TR
INH/UVLO
VOUT
STSEL
SS/TR
INH/UVLO
VOUT
STSEL
V
OUT1
R1
R2
V
OUT2
( )
( )
´
= W
OUT2
V 12.6
R1 k
0.6
( )
( )
´
= W
-
OUT2
0.6 R1
R2 k
V 0.6
STSEL
INH/UVLO
PWRGD
VOUT
V
OUT1
STSEL
INH/UVLO
PWRGD
VOUT
V
OUT2
LMZ31704
www.ti.com SLVSBV8A –JUNE 2013–REVISED AUGUST 2013
Sequencing (SS/TR)
Many of the common power supply sequencing methods can be implemented using the SS/TR, INH and
PWRGD pins. The sequential method is illustrated in Figure 36 using two LMZ31704 devices. The PWRGD pin
of the first device is coupled to the INH pin of the second device which enables the second power supply once
the primary supply reaches regulation. Figure 37 shows sequential turn-on waveforms of two LMZ31704 devices.
Figure 36. Sequencing Schematic Figure 37. Sequencing Waveforms
Simultaneous power supply sequencing can be implemented by connecting the resistor network of R1 and R2
shown in Figure 38 to the output of the power supply that needs to be tracked or to another voltage reference
source. The tracking voltage must exceed 750mV before V
OUT2
reaches its set-point voltage. The PWRGD output
of the V
OUT2
device may remain low if the tracking voltage does not exceed 1.4V.Figure 39 shows simultaneous
turn-on waveforms of two LMZ31704 devices. Use Equation 3 and Equation 4 to calculate the values of R1 and
R2.
(3) (4)
Figure 38. Simultaneous Tracking Schematic Figure 39. Simultaneous Tracking Waveforms
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