Diodes ZLDO485 - Manual (Page 8)

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
f o r t h e s y s t e m s u p pl ie d t o s h u t do 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
SC
Vin
N/C
Gnd
ZLDO485
6V C2
1uF
C1
10pF
C3
100nF
R1
100k
0V
+ 4.85V
Microproc.
System
Interrupt
Input
APPLICATIONS
Figure 4
4-78