SP703 Datasheet, PDF (11/16 Pages) Sipex Corporation – Low Power Microprocessor Supervisory with Battery Switch-Over

SIGNAL
STATUS
V_CC
V_OUT
Disconnected from V_OUT
Connected to V_BATT through
an internal 8Ω PMOS switch
V_BATT
PFI
Connected to V_OUT. Current
drawn from the battery is
less than 0.6µA, as long as
V_CC < V_BATT - 1V.
Power-fail comparator is
disabled.
PFO Logic low
RESET Logic low
MR Manual Reset is disabled
Figure 10. Input and Output Status in Battery-Backup Mode.
To enter the Battery-Backup mode, V_CC must be less than the
Reset threshold and less than V_BATT.
Using a High Capacity Capacitor
as a Backup Power Source
VBATT has the same operating voltage range as
VCC, and the battery-switchover threshold volt-
ages are typically +20mV centered at VBATT,
allowing use of a capacitor and a simple charg-
ing circuit as a backup source (see Figure 12).
PART
NUMBER
MAXIMUM
BACKUP-BATTERY
VOLTAGE [V]
SP703
4.80
SP704
4.55
Figure 11. Allowable BACKUP-BATTERY Voltages
+5V
VCC
VBATT _SP703
VOUT
CONNECT TO
STATIC RAM
0.1F
RESET
GND
CONNECT
TO µP
Figure 12. Backup Power Source Using High Capacity
Capacitor with SP703 and a +5V ±5% Supply
If VCC is above the reset threshold and VBATT
is 0.5V above VCC, current flows to V_OUT and
VCC from VBATT until the voltage at VBATT is
less than 0.5V above VCC.
Leakage current through the capacitor charging
diode and the SP703/704 internal power
diode eventually discharges the capacitor to
VCC. Also, if VCC and VBATT start from 0.5V
above the reset threshold and power is lost
at VCC, the capacitor on VBATT discharges
through VCC until VBATT reaches the reset
threshold; the SP703/704 then switches to
battery-backup mode.
+5V
VCC
VBATT _SP704
VOUT
CONNECT TO
STATIC RAM
0.1F
100KΩ
RESET
GND
CONNECT
TO µP
Figure 13. Backup Power Source Using High Capacity
Capacitor with SP704 and a +5V ±10% Supply
SP703/704DS/07
SP703/704 Low Power Microprocessor Supervisory
11
© Copyright 2000 Sipex Corporation