SP690A 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
RESET Logic high (SP805 only)
WDI Watchdog timer is disabled
Figure 14. 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 charging
circuit as a backup source (see Figure 16).
PART
NUMBER
MAXIMUM
BACKUP-BATTERY
VOLTAGE [V]
SP690A
SP802L
4.80
SP805L
SP692A
SP802M
4.55
SP805M
Figure 15. Allowable BACKUP-BATTERY Voltages
+5V
VBATT
VCC
VOUT
CONNECT TO
STATIC RAM
0.1F
RESET CONNECT
(RESET)* TO µP
GND _{*( ) SP805L only}
Figure 16. Backup Power Source Using High Capacity
Capacitor with SP690A/802L/805L and a +5V ±5% Supply
If VCC is above the reset threshold and VBATT
is 0.5V above VCC, current flows to VOUT 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 SP690A/SP802L/SP805L 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
SP690A/SP802L/SP805L then switches to
battery-backup mode.
+5V
VBATT
0.1F
100KΩ
VCC
VOUT
CONNECT TO
STATIC RAM
RESET ^CONNECT
(RESET)* TO µP
GND
*( ) SP805M only
Figure 17. Backup Power Source Using High Capacity
Capacitor with SP692A/802M/805M and a +5V ±10% Supply
Date: 11/29/04
SP690A/692A Low Power Microprocessor Supervisory with Battery Switch-Over
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