MAX791CSE+ Maxim Integrated Products, MAX791CSE+ Datasheet - Page 12

• Manufacturer Part Number: MAX791CSE+
• Description: IC MPU SUPERVISOR CIRCUIT 16SOIC
• Manufacturer: Maxim Integrated Products
• Type: Battery Backup Circuitr

Specifications of MAX791CSE+

• Number Of Voltages Monitored: 1
• Output: Push-Pull, Totem Pole
• Reset: Active Low
• Reset Timeout: 140 ms Minimum
• Voltage - Threshold: 4.65V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Monitored Voltage: 4.65 V
• Undervoltage Threshold: 4.5 V
• Overvoltage Threshold: 4.75 V
• Manual Reset: Resettable
• Watchdog: Yes
• Battery Backup Switching: Yes
• Power-up Reset Delay (typ): 280 ms
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 0 V
• Supply Current (typ): 150 uA
• Maximum Power Dissipation: 696 mW
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 70 C
• Chip Enable Signals: Yes
• Minimum Operating Temperature: 0 C
• Output Type: Active Low or Open Drain or Push-Pull
• Power Fail Detection: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PFI is the input to the power-fail comparator. PFI has a
guaranteed input leakage of ±25nA max over tempera-
ture. The typical comparator delay is 15µs from V
V
being restored). If unused, connect this input to
ground.
The Power-Fail Output (PFO) goes low when PFI goes
below 1.25V. It typically sinks 3.2mA with a saturation
voltage of 0.1V. With PFI above 1.25V, PFO is actively
pulled to V
divider to an unregulated supply allows PFO to gener-
ate an NMI as the unregulated power begins to fall
(Figure 9b). If the unregulated supply is inaccessible,
Microprocessor Supervisory Circuit
Figure 9. a) If the unregulated supply is inaccessible,
LOWLINE generates the NMI for the µP. b) Use PFO to gener-
ate the µP NMI if the unregulated supply is inaccessible.
12
OL
REGULATED
a)
b)
SUPPLY
FROM
(power failing), and 55µs from V
______________________________________________________________________________________
REGULATOR
0.1µF
VOLTAGE
OUT
3
V
CC
. Connecting PFI through a voltage-
0.1
µF
7
3
MAX791
4
GND
PFI
V
LOWLINE
CC
VBATT
RESET
MAX791
V
4
WDI
GND
OUT
VBATT
RESET
2
1
15
10
11
V
PFO
WDI
OUT
2
1
15
6
11
3.0V
0.1µF
Power-Fail Output
3.0V
0.1µF
IH
Power-Fail Input
RESET
NMI
I/O LINE
POWER TO
CMOS RAM
µP POWER
to V
µP
RESET
NMI
I/O LINE
POWER TO
CMOS RAM
OH
µP POWER
µP
(power
IL
to
use LOWLINE to generate the NMI. The LOWLINE
threshold is typically 150mV above the reset threshold
(see LOWLINE Output section).
The MAX791 requires two conditions to switch to bat-
tery-backup mode: 1) V
threshold; 2) V
the status of the inputs and outputs in battery-backup
mode.
Table 1. Input and Output States in
Battery-Backup Mode
* V
backup mode.
PIN
10
11
12
13
14
15
16
CC
1
2
3
4
5
6
7
8
9
must be below the reset threshold to enter battery-
–
—
L
BATT ON
–
C
O
—
VBATT
–
R
–
W
NAME
—
—
–
C
V
–
W
GND
E
—
—
–
P
SWT
–
V
WDI
—
W
E
—
PFI
–
M
—
D
OUT
E
—
–
—
F
—
CC
—
D
S
OUT
—
—
L
R
—
P
O
–
—
IN
—
E
–
O
—
CC
I
–
O
N
T
–
–
—
E
–
must be below VBATT. Table 1 lists
Supply current is 1µA maximum.
V
an internal PMOS switch.
Battery-switchover comparator
monitors V
GND—0V reference for all signals.
Logic high. The open-circuit output is
equal to V
The power-fail comparator remains
active in the battery-backup mode for
V
voltage,
The power-fail comparator remains
active in the battery-backup mode for
V
SWT is ignored.
– –
M
Logic low*
WDI is ignored, and goes high
impedance.
Logic high. The open-circuit output
voltage is equal to V
High impedance
Logic high. The open-circuit output
voltage is equal to V
Logic low*
Logic high. The open-circuit output
voltage is equal to V
—
OUT
CC
CC
R
–
is ignored.
≥ VBATT - 1.2V typ. Below this
≥ VBATT - 1.2V typ.
CC
is connected to VBATT through
Battery-Backup Mode
–
P
—
must be below the reset
F
OUT
—
CC
O
–
is forced low.
for active switchover.
.
STATUS
OUT
OUT
OUT
.
.
.