SP690RCN SIPEX [Sipex Corporation], SP690RCN Datasheet - Page 14

• Manufacturer Part Number: SP690RCN
• Description: 3.0V/3.3V Low Power Microprocessor Supervisory with Battery Switch-Over
• Manufacturer: SIPEX [Sipex Corporation]

Figure 21. Using a High Capacity Capacitor as a Backup Power Source
Switchover at V
backup mode is entered before V
close to the 2.0V minimum required to reliably
retain data in CMOS RAM. Switchover at higher
V
life. When V
until V
to ensure a stable supply. V
V
Using a High Capacity Capacitor as a
Backup Power Source
Figure 21 shows two ways to use a High Value
Capacitor as a backup power source. The High
Value Capacitor may be connected through a
diode to the 3V input as in Figure 21A or, if a
5V supply is also available, the High Value
Capacitor may be charged up to the 5V supply
as in Figure 21B allowing a longer backup
period. Since V
is above the reset threshold, there are no
special precautions when using these
supervisors with a High Value Capacitor.
Operation Without a Backup Power
Source
These
battery-backed applications. If a backup power
source is not used, connect both VBATTERY
and V
switch over to any backup power source, V
does not need to be switched. A direct connec-
tion to V
the switch which may push V
SP690T/S/R DS/10
A)
CC
CC
1N4148
0.1F
through a 1.5 PMOS power switch.
voltages would decrease backup-battery
OUT
CC
CC
P supervisors were designed for
rises above the reset threshold, V
V
to V
BATTERY
eliminates any voltage drops across
CC
3.0V or 3.3V
SP690T/S/R, 802/T/S/R, 804T/S/R, 805T/S/R Low Power Microprocessor Supervisory
BATTERY
recovers, switchover is deferred
CC
SW
. Since there is no need to
(2.40V) ensures that battery-
V
GND
CC
can exceed V
V
pin 7*
OUT
OUT
OUT
CONNECT TO
is connected to
STATIC RAM
below V
CONNECT
OUT
CC
TO P
while V
gets too
CC
RST
OUT
CC
.
P
,
14
Replacing the Backup Battery
If V
to ground, the backup battery can be removed
while V
triggering RESET/RESET. As long as V
stays above V
be entered.
Adding Hysteresis to the Power-Fail
Comparator
The power-fail comparator has a typical input
hysteresis of 10mV. This is sufficient for most
applications where a power-supply line is being
monitored through an external voltage divider
(refer to the Monitoring an Additional Power
Supply section).
If additional noise margin is desired, connect a
resistor between PFO and PFI as shown in
Figure 22A. Select the ratio of R1 and R2 such
that PFI sees 1.25V when V
point (V
typically be more than 10 times the value of R1
or R2. The hysteresis window extends both
above (V
point (V
1N4148
B)
0.1F
BATTERY
+5V
TRIP
V
CC
TRIP
BATTERY
H
) and below (V
*
is decoupled with a 0.1 F capacitor
remains valid without danger of
).
). R3 adds the hysteresis and will
3.0V or 3.3V
RESET for the SP690T/S/R and the SP802T/S/R
RESET for the SP804T/S/R and the SP805T/S/R
SW
, battery-backup mode cannot
V
GND
CC
V
pin 7*
© Copyright 2000 Sipex Corporation
OUT
L
) the original trip
IN
CONNECT TO
STATIC RAM
CONNECT
falls to its trip
TO P
CC