參數(shù)資料
型號: MAX791EJE
廠商: MAXIM INTEGRATED PRODUCTS INC
元件分類: 電源管理
英文描述: Microprocessor Supervisory Circuit
中文描述: 1-CHANNEL POWER SUPPLY MANAGEMENT CKT, CDIP16
封裝: 0.300 INCH, CERAMIC, DIP-16
文件頁數(shù): 13/20頁
文件大?。?/td> 146K
代理商: MAX791EJE
Battery-Bac kup Mode
The MAX791 requires two conditions to switch to bat-
tery-backup mode: 1) V
CC
must be below the reset
threshold; 2) V
CC
must be below VBATT. Table 1 lists
the status of the inputs and outputs in battery-backup
mode.
Battery On Output
The Battery On (BATT ON) output indicates the status
of the internal V
CC
/battery-switchover comparator,
which controls the internal V
CC
and VBATT switches.
For V
CC
greater that VBATT (ignoring the small hystere-
sis effect), BATT ON typically sinks 3.2mA at 0.1V satu-
ration voltage. In battery-backup mode, this terminal
sources approximately 10μA from V
OUT
. Use BATT ON
to indicate battery-switchover status or to supply base
drive to an external pass transistor for higher-current
applications (see Typical Operating Circuit.
Input S upply V oltage
The Input Supply Voltage (V
CC
) should be a regulated
+5V. V
CC
connects to V
OUT
via a parallel diode and a
large PMOS switch. The switch carries the entire cur-
rent load for currents less than 250mA. The parallel
diode carries any current in excess of 250mA. Both the
switch and the diode have impedances less than 1
each (Figure 10). The maximum continuous current is
250mA, but power-on transients may reach a maximum
of 1A.
Bac kup-Battery Input
The Backup-Battery Input (VBATT) is similar to V
CC
,
except the PMOS switch and parallel diode are much
smaller. Accordingly, the on-resistances of the diode
and the switch are each approximately 10
.
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 S upply V oltage
The Output Supply Voltage (V
OUT
) is internally connect-
ed to the substrate of the IC and supplies all the current
to the external system and internal circuitry. All open-
circuit outputs will, for example, assume the V
OUT
volt-
age in their high states rather than the V
CC
voltage. At
the maximum source current of 250mA, V
OUT
will typi-
cally be 200mV below V
CC
. Decouple this terminal with
a 0.1μF capacitor.
M
Mic roproc essor S upervisory Circ uit
______________________________________________________________________________________
13
200ms TYP
RESET
THRESHOLD
V
CC
RESET
CE IN
CE OUT
SECOND CE PULSE ABSENT WHEN VBATT < 2V
Figure 11. Backup-Battery Monitor Timing Diagram
MAX791
VBATT
V
CC
1
3
2
0.1
μ
F
V
OUT
Figure 10. V
CC
and VBATT-to-V
OUT
Switch
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