LMZ31710 Datasheet, PDF (24/33 Pages) Texas Instruments – 10A SIMPLE SWITCHER® Power Module with 2.95V-17V Input and Current Sharing in QFN Package

LMZ31710
SNVS987A – JULY 2013 – REVISED JULY 2013
www.ti.com
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 39 using two LMZ31710 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 40 shows sequential turn-on waveforms of two LMZ31710 devices.
INH/UVLO
STSEL
VOUT
PWRGD
VOUT1
INH/UVLO
STSEL
VOUT
PWRGD
VOUT2
Figure 39. Sequencing Schematic
Figure 40. Sequencing Waveforms
Simultaneous power supply sequencing can be implemented by connecting the resistor network of R1 and R2
shown in Figure 41 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 42 shows simultaneous
turn-on waveforms of two LMZ31710 devices. Use Equation 3 and Equation 4 to calculate the values of R1 and
R2.
R1 = ^{(VOUT2 ´12.6)} (kW)
0.6
(3)
R2
=
0.6 ´ R1
(V_OUT2 - 0.6)
(kW)
(4)
VOUT
INH/UVLO
STSEL
SS/TR
V_OUT1
VOUT
INH/UVLO
STSEL
SS/TR
V_OUT2
R1
R2
Figure 41. Simultaneous Tracking Schematic
Figure 42. Simultaneous Tracking Waveforms
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