LP3907 Datasheet, PDF (24/44 Pages) National Semiconductor (TI) – Dual High-Current Step-Down DC/DC and Dual Linear Regulator with I2C Compatible Interface

Faults Occurring in Counter Delay After Startup
The above timing diagram details the Power good with delay
with respect to the enable signals EN1, and EN2. The RDY1,
RDY2 are internal signals derived from the output of two com-
parators. Each comparator has been trimmed as follows:
Comparator Level
Buck Supply Level
HIGH
Greater than 94%
LOW
Less than 85%
The circuits for EN1 and RDY1 is symmetrical to EN2 and
RDY2, so each reference to EN1 and RDY1 will also work for
EN2 and RDY2 and vice versa.
30017881
If EN1 and RDY1 signals are High at time t1, then the RDY1
signal rising edge triggers the programmable delay counter
(50μs, 50ms, 100ms, 200ms). This delay forces nPOR LOW
between time interval t1 and t2. nPOR is then pulled high after
the programmable delay is completed. Now if EN2 and RDY2
are initiated during this interval the nPOR signal ignores this
event.
If either RDY1or RDY2 were to go LOW at t3 then the pro-
grammable delay is triggered again.
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