ZLDO485 datasheet(8/9 Pages) ZETEX

8 / 9 page

ZLDO485

5). Low Battery Flag

The ZLDO485 provides an output called Low

Battery Flag (LBF). Unlike many regulators that

only signal that they are falling out of

regulation, the LBF output of the ZLDO485

series indicates that the voltage drop across

the regulator has fallen to less than typically

300mV and so supply failure is imminent.

This improved warning gives both more time

for the system suppl ied to shutdo wn

gracefully and maintains regulation while this

happens. This could be a vital point if

measurements are under way and must be

completed accurately for instance. The LBF

output is driven by an open collector NPN

transistor which pulls low when the supply to

the regulator is failing. Fig.4 shows this output

being used. Note that resistor R1 is necessary

only if the interrupt logic does not include a

pull-up resistor.

Spg

D/C

Vout

LBF

Vin

N/C

Gnd

ZLDO485

1uF

10pF

100nF

100k

+4.85V

Microproc.

System

Interrupt

Input

APPLICATIONS

Figure 4

4-78

ZLDO485 Datasheet(PDF) 8 Page - Zetex Semiconductors