sp691a Exar Corporation, sp691a Datasheet - Page 16

• Manufacturer Part Number: sp691a
• Description: Low Power Microprocessor Supervisory With Battery Switch-over
• Manufacturer: Exar Corporation

Figure 25. High Capacity Capacitor on V
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 (V
the current to the external system and internal
circuitry. All open-circuit outputs will assume
the V
the V
current of 250mA, V
150mV below V
with 0.1µF capacitor.
TYPICAL APPLICATIONS
The SP691A/693A/800L/800M devices are not
short-circuit protected. Shorting V
ground, other than power-up transients such as
charging a decoupling capacitor, may destroy
the device. All open-circuit outputs swing
between V
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
Date: 4/18/05
+5V
1N4148
0.47F
OUT
powered from V
from V
currents flow from the battery.
CC
voltage in their high states rather than
voltage. At the maximum source
OUT
CC
SP691A/693A/800L/800M Low Power Microprocessor Supervisor with Battery Switch-Over © Copyright 2005 Sipex Corporation
1
and GND rather than V
CC
is 35µA, while only leakage
. V
V
BATT
CC
OUT
OUT
. Typical supply current
GND
Corporation
should be decoupled
Vcc
4
will typically be
3
OUT
V
OUT
) supplies all
BATT
2
OUT
CC
and
to
16
2) Battery-backup mode where V
3) Battery-backup mode where V
Using High Capacity Capacitor with the
SP691A/693A/800L/800M Series
V
V
voltages are typically +30mV centered at V
allowing use of a capacitor and a simple
charging circuit as a backup source. Refer to
Figure 25.
If V
is 0.5V above V
V
less than 0.5V above V
Leakage current through the capacitor charging
diode and SP691A/693A/800L/800M internal
power diode eventually discharges the capacitor
to V
above the reset threshold and power is lost at
V
V
SP691A/693A/800L/800M devices then switch
to battery-backup mode.
Using Separate Power Supplies for V
and V
If using separate power supplies for V
V
V
As described in the previous section, if V
exceeds this limit and power is lost at V
current flows continuously from V
V
V
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
BATT
CC
CC
CC
BATT
CC
OUT
CC
CC
CC
CC
, the capacitor on V
, and the battery-switchover threshold
until V
from V
within 0.7V below V
powered from V
current from the battery is typically less
than 5µA.
V
current is less than 1µA max.
when V
via the V
-to-V
CC
. Also, if V
, V
BATT
has the same operating voltage range as
is above the reset threshold and V
BATT
CC
IN
BATT
by at least 0.7V. V
BATT
to ground, pull up CE
CC
switch until the circuit is broken.
BATT
must be less than 0.3V above
CC
reaches the reset threshold; the
is above the reset threshold.
CC
until the voltage at V
, current flows to V
and V
-to-V
BATT
CC
BATT
.
BATT
BATT
OUT
discharges through
and the supply
. All circuitry is
start from 0.5V
diode and the
CC
CC
BATT
OUT
is typically
is less than
to V
OUT
BATT
supply
BATT
CC
BATT
BATT
BATT
OUT
and
BATT
and
CC
to
is
,
,
,