SP703 SIPEX [Sipex Corporation], SP703 Datasheet - Page 10

• Manufacturer Part Number: SP703
• Description: Low Power Microprocessor Supervisory with Battery Switch-Over
• Manufacturer: SIPEX [Sipex Corporation]

Power-Fail Comparator
The Power-Fail Comparator can be used as an
under-voltage detector to signal the failing of a
power supply (it is completely separate from the
rest of the circuitry and does not need to be
dedicated to this function). The PFI input is
compared to an internal 1.25V reference. If PFI
is less than 1.25V, PFO goes low. The external
voltage divider drives PFI to sense the unregu-
lated DC input to the +5V regulator. The volt-
age-divider ratio can be chosen such that the
voltage at PFI falls below 1.25V just before the
+5V regulator drops out. PFO then triggers an
interrupt which signals the P to prepare for
power-down.
When V
comparator is turned off and PFO is forced low
to conserve backup-battery power.
Figure 9. BACKUP-BATTERY Switchover Block Diagram
SP703/704DS/07
Reset Threshold = 4.65V in SP703
Reset Threshold = 4.40V in SP704
V
V
V
V
V
C
C
C
C
C
C
C
C
C
C
>
<
>
<
<
C
R
R
V
R
V
s e
s e
s e
SW1
O
B
B
V
A
A
BATT
N
t e
t e
T
t e
T
OUT
T
T
D
T
T
T
I
r h
r h
r h
T
V
s e
s e
s e
connects to V
I
O
BATT
o h
o h
o h
N
d l
d l
d l
GND
D1
a
a
d n
d n
D3
V
CC
l C
D2
O
O
S
OUT
W
s o
p
p
n e
n e
d e
1
, the power-fail
SP703/704 Low Power Microprocessor Supervisory
SW2
l C
l C
O
S
W
s o
s o
p
n e
d e
d e
2
10
Backup-Battery Switchover
In the event of a brownout or power failure, it
may be necessary to preserve the contents of
RAM. With a backup battery installed at V
the RAM is assured to have power if V
As long as V
V
power switch. Once V
threshold, V
switches to V
through a 5 switch only when V
reset threshold and V
When V
connected to V
applied to V
the diode (D1) between V
conduct current from V
more than .6V above V
When V
activated and the internal circuitry will be
powered from the battery Figure 10. When V
is just below V
current drawn from V
30 A. When V
V
off and the supply current falls to less than 0.6 A.
OUT
BATT
connects to V
, the internal switchover comparator shuts
BATT
CC
exceeds the reset threshold, it is
CC
BATT
connects to V
CC
OUT
or V
CC
OUT
BATT
exceeds the reset threshold,
. V
drops to more than 1V below
Figure 9. During this time,
, regardless of the voltage
BATT
CC
, in the backup mode the
BATT
BATT
BATT
© Copyright 2000 Sipex Corporation
CC
through a 0.6
OUT
BATT
, whichever is higher,
falls below the reset
is greater than V
OUT
BATT
.
to V
connects to V
will be typically
, backup mode is
OUT
and V
CC
is below the
if V
OUT
CC
PMOS
BATT
BATT
fails.
will
OUT
CC
CC
is
.
,