SP691A Datasheet, PDF (16/24 Pages) Sipex Corporation – Low Power Microprocessor Supervisory with Battery Switch-Over

+5V
1N4148
0.47F
3
Vcc
1
VBATT
2
VOUT
Corporation
GND
4
Figure 25. High Capacity Capacitor on V_BATT
Continuous current should be limited to 25mA
and peak currents (only during power-up)
limited to 250mA. The reverse leakage of this
input is less than 1µA over temperature and
supply voltage.
Output Supply Voltage
The Output Supply Voltage (VOUT) supplies all
the current to the external system and internal
circuitry. All open-circuit outputs will assume
the VOUT voltage in their high states rather than
the VCC voltage. At the maximum source
current of 250mA, VOUT will typically be
150mV below VCC. VOUT should be decoupled
with 0.1µF capacitor.
TYPICAL APPLICATIONS
The SP691A/693A/800L/800M devices are not
short-circuit protected. Shorting VOUT to
ground, other than power-up transients such as
charging a decoupling capacitor, may destroy
the device. All open-circuit outputs swing
between VOUT and GND rather than VCC and
GND. If long leads connect to the chip inputs,
ensure that these lines are free from ringing and
other conditions that would forward bias the
chip's protection diodes.
There are three distinct modes of operation:
1) Normal operating mode with all circuitry
powered from V . Typical supply current
CC
from V_CC is 35µA, while only leakage
currents flow from the battery.
2) Battery-backup mode where V_CC is typically
within 0.7V below V_BATT. All circuitry is
powered from V_BATT and the supply
current from the battery is typically less
than 5µA.
3) Battery-backup mode where V_CC is less than
V_BATT by at least 0.7V. V_BATT supply
current is less than 1µA max.
Using High Capacity Capacitor with the
SP691A/693A/800L/800M Series
VBATT has the same operating voltage range as
VCC, and the battery-switchover threshold
voltages are typically +30mV centered at VBATT,
allowing use of a capacitor and a simple
charging circuit as a backup source. Refer to
Figure 25.
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 SP691A/693A/800L/800M 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
SP691A/693A/800L/800M devices then switch
to battery-backup mode.
Using Separate Power Supplies for V_BATT
and V_CC
If using separate power supplies for VCC and
VBATT, VBATT must be less than 0.3V above
VCC when VCC is above the reset threshold.
As described in the previous section, if VBATT
exceeds this limit and power is lost at VCC,
current flows continuously from VBATT to
VCC via the VBATT-to-VOUT diode and the
VOUT-to-VCC switch until the circuit is broken.
Refer to Figure 24.
Alternative Chip-Enable Gating
Using memory devices with CE and CE inputs
allows the CE loop of the SP691A/693A/800L/
800M series to be bypassed. To do this,
connect CE_IN to ground, pull up CE_OUT to VOUT,
Date: 5/25/04
SP691A/693A/800L/800M Low Power Microprocessor Supervisor with Battery Switch-Over © Copyright 2004 Sipex Corporation
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