SP791CN SIPEX [Sipex Corporation], SP791CN Datasheet - Page 14

• Manufacturer Part Number: SP791CN
• Description: Low Power Microprocessor Supervisory with Battery Switch-Over
• Manufacturer: SIPEX [Sipex Corporation]

LOW-BATTERY MONITOR
The SP791 low-battery voltage function moni-
tors V
timeout period (200ms) that occurs either after
a normal power-up sequence or after the MR
reset input has been returned to its high state. If
the battery voltage is below 2.0V, the second
CE pulse is inhibited after reset timeout. If the
battery voltage is above 2.0V, all CE pulses are
allowed through the CE gate after the reset
timeout period. To use this function, after the
200ms reset delay, write 00 (HEX) to a loca-
tion using the first CE pulse, and write FF (HEX)
to the same location using the second CE pulse
following RESET going inactive on power-up.
The contents of the memory then indicates a
good battery (FF) or a low battery (00),
Figure 11.
TYPICAL APPLICATIONS
The SP791 is not short-circuit protected. Short-
ing V
sients such as charging a decoupling capacitor,
may destroy the device. All open-circuit out-
puts swing between V
V
inputs, ensure that these lines are free from ring-
ing and other conditions that would forward bias
the chip's protection diodes.
SP791DS/08
Figure 11. Backup-Battery Monitor Timing Diagram
THRESHOLD
0.15V is monitored only during the reset-
CC
CE
RESET
CE
and GND. If long leads connect to the chip
OUT
RESET
OUT
Vcc
IN
BATT
SECOND CE PULSE ABSENT WHEN V
to ground, other than power-up tran-
. Low-battery detection of 2.0V
200ms TYP
SP791 Low Power Microprocessor Supervisory with Battery Switch-Over
OUT
and GND rather than
BATT
< 2V
14
There are three distinct modes of operation:
1) Normal operating mode with all circuitry
2) Battery-backup mode where V
3) Battery-backup mode where V
USING HIGH CAPACITY CAPACITOR
WITH THE SP791
V
V
ages are typically +30mV centered at V
allowing use of a capacitor and a simple charg-
ing circuit as a backup source (see Figure 12).
If V
is 0.5V above V
V
less than 0.5V above V
Figure 12. High Capacity Capacitor on VBATT
™ - REGISTERED TRADEMARK OF BAKNOR INDUSTRIES
BATT
CC
CC
CC
, and the battery-switchover threshold volt-
from V
powered up from V
current from V
leakage currents flow from the battery.
within 0.7V below V
powered up from V
current is typically less than 40 A.
V
current is less than 1 A.
+5V
1N4148
0.47F
BATT
has the same operating voltage range as
is above the reset threshold and V
BATT
by at least 0.7V. V
CC
1
until the voltage at V
, current flows to VOUT and
V
CC
BATT
© Copyright 2000 Sipex Corporation
CC
is 40 A, while only
BATT
.
GND
BATT.
Corporation
CC
Vcc
4
3
. Typical supply
V
, and the supply
OUT
All circuitry is
CC
CC
BATT
2
is typically
is less than
BATT
supply
BATT
BATT
is
,