LM26480 datasheet(18/30 Pages) NSC

Part #	LM26480

Description	Externally Programmable Dual High-Current Step-Down DC/DC and Dual Linear Regulators

PDF	30 Pages

Scroll/Zoom	100%

Manufacturer	NSC [National Semiconductor (TI)]

Direct Link	http://www.national.com

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18 / 30 page

Faults Occurring in Counter Delay After Startup

30040407

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 91%

LOW

Less than 82%

The circuits for EN1 and RDY1 are symmetrical to EN2 and

RDY2, so each reference to EN1 and RDY1 will also work for

EN2 and RDY2 and vice versa.

If EN1 and RDY1 signals are High at time t1, then the RDY1

signal rising edge triggers the programmable delay counter

(50

μs, 50 ms, 100 ms, 200 ms). 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.

LM26480 Datasheet(PDF) 18 Page - National Semiconductor (TI)