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參數(shù)資料
| 型號： | SP791EP |
| 英文描述： | Low Power Microprocessor Supervisory with Battery Switch-Over |
| 中文描述： | 低功耗微處理器監(jiān)控與電池開關過 |
| 文件頁數(shù)： | 14/19頁 |
| 文件大?。?/td> | 202K |
| 代理商： | SP791EP |
SP791DS/08 SP791 Low Power Microprocessor Supervisory with Battery Switch-Over
Copyright 2000 Sipex Corporation
14
There are three distinct modes of operation:
1) Normal operating mode with all circuitry
powered up from V
CC
. Typical supply
current from V
CC
is 40
μ
A, 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 up from V
BATT
, and the supply
current is typically less than 40
μ
A.
3) Battery-backup mode where V
CC
is less than
V
BATT
by at least 0.7V. V
BATT
supply
current is less than 1
μ
A.
USING HIGH CAPACITY CAPACITOR
WITH THE SP791
V
BATT
has the same operating voltage range as
V
CC
, and the battery-switchover threshold volt-
ages are typically +30mV centered at V
BATT
,
allowing use of a capacitor and a simple charg-
ing circuit as a backup source (see
Figure 12)
.
If V
CC
is above the reset threshold and V
BATT
is 0.5V above V
CC
, current flows to VOUT and
V
CC
from V
BATT
until the voltage at V
BATT
is
less than 0.5V above V
CC
.
LOW-BATTERY MONITOR
The
SP791
low-battery voltage function moni-
tors V
BATT
. Low-battery detection of 2.0V
±
0.15V is monitored only during the reset-
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
OUT
to ground, other than power-up tran-
sients such as charging a decoupling capacitor,
may destroy the device. All open-circuit out-
puts swing between V
OUT
and GND rather than
V
CC
and GND. If long leads connect to the chip
inputs, ensure that these lines are free from ring-
ing and other conditions that would forward bias
the chip's protection diodes.
Figure 12. High Capacity Capacitor on VBATT
Figure 11. Backup-Battery Monitor Timing Diagram
RESET
Vcc
200ms TYP
RESET
CE
IN
CE
OUT
SECOND CE PULSE ABSENT WHEN V
BATT
< 2V
(
C orporation
+5V
1N4148
0.47F
1
3
2
4
Vcc
V
BATT
V
OUT
GND
- REGISTERED TRADEMARK OF BAKNOR INDUSTRIES
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