MAX808N Maxim Integrated Products, MAX808N Datasheet - Page 9

• Manufacturer Part Number: MAX808N
• Description: (MAX801x / MAX808x) Supervisory Circuits
• Manufacturer: Maxim Integrated Products

calculate the amount of capacitance required to allow
the shutdown routine to complete before reset is
asserted:
where t
plete the shutdown routine (including the V
line propagation delay), I
drained from the capacitor, and V
reset threshold.
The output supply (OUT) transfers power from V
BATT to the µP, RAM, and other external circuitry. At
the maximum source current of 250mA, V
cally be 220mV below V
capacitor to ground.
Battery-backup mode preserves the contents of RAM in
the event of a brownout or power failure. With a backup
battery installed at BATT, the MAX801/MAX808 automati-
cally switches RAM to backup power when V
Two conditions are required for switchover to battery-
backup mode: 1) V
2) V
inputs and outputs during battery-backup mode.
BATT is designed to conduct up to 20mA to OUT dur-
ing battery backup. The PMOS switch on-resistance is
approximately 12Ω. Figure 4 shows the two series pass
elements (between the BATT input and OUT) that
facilitate UL recognition. V
normal operation without causing a reset.
Figure 3. Using LOWLINE to Provide a Power-Fail Warning to
the µP
CC
REGULATOR
C
C
SHDN
must be below V
HOLD
HOLD
> I
LOAD
is the time required for the system to com-
C
= (I
HOLD
4.5V to 5.5V
V
x t
LR
SHDN
LOAD
_______________________________________________________________________________________
CC
must be below the reset threshold;
CC
x t
BATT
V
BATT
SHDN
Output Supply Voltage
. Decouple OUT with a 0.1µF
CC
LOAD
Battery-Backup Mode
MAX801
MAX808
. Table 1 lists the status of
GND
can exceed V
) / (V
LOWLINE
is the current being
LR
LR(min)
is the low-line to
OUT
)
CC
CC
8-Pin µP Supervisory Circuits
TO P NMI
CC
will typi-
to low-
with ±1.5% Reset Accuracy
during
CC
falls.
or
Figure 4. V
Table 1. Input and Output Status in
Battery-Backup Mode
MAX801 MAX808
—
—
1
2
3
4
5
6
7
8
BATT
V
CC
PIN
CC
—
—
1
2
3
4
5
6
7
8
and BATT to OUT Switch
CIRCUITRY
CONTROL
LOWLINE
CE OUT
RESET
NAME
RESET
CE IN
BATT
GND
OUT
WDI
V
CC
P
P
Battery switchover
comparator monitors V
for active switchover.
Logic low
Logic low
Ground—0V reference for
all signals
Logic high; the open-circuit
voltage is equal to V
Logic high. The open-circuit
output voltage is equal to
V
WDI is ignored and goes
high impedance.
High impedance (MAX808)
Supply current is 1µA max for
V
OUT is connected to BATT
through two internal PMOS
switches in series.
BATT
BATT
MAX801
MAX808
(MAX808).
≤ 2.8V.
P
STATUS
CC
0.1 F
CC
OUT
.
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