LP3907-Q1 Datasheet, PDF (22/53 Pages) Texas Instruments – Dual High-Current Step-Down DC-DC And Dual Linear Regulator

LP3907-Q1
SNVSA55A – DECEMBER 2014 – REVISED MAY 2015
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Case1
t1
t2
EN1
EN2
RDY1
RDY2
0V
Counter
nPOR
delay
Case2
t1
t2
EN1
EN2
RDY1
0V
RDY2
nPOR
Counter
delay
Case3
EN1
EN2
RDY1
RDY2
nPOR
t1
t2
Counter
delay
Figure 35. nPOR with Counter Delay
Figure 35 shows the simplest application of the Power On Reset, where both switcher enables are tied together.
In Case 1, EN1 causes nPOR to transition LOW and triggers the nPOR delay counter. If the power supply for
Buck2 does not come on within that period, nPOR stays LOW, indicating a power fail mode. Case 2 indicates the
vice versa scenario if Buck1 supply did not come on. In both cases the nPOR remains LOW.
Case 3 shows a typical application of the Power On Reset, where both switcher enables are tied together. Even
if RDY1 ramps up slightly faster than RDY2 (or vice versa), then nPOR signal triggers a programmable delay
before going HIGH, as explained below.
22
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