SP791CN SIPEX [Sipex Corporation], SP791CN Datasheet - Page 12

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

LOWLINE OUTPUT
The low-line comparator monitors V
typical threshold voltage 150mV above the re-
set threshold and has 15mV of hysteresis.
LOWLINE typically sinks 3.2mA at 0.1V. For
normal operation (Vcc above the LOWLINE
threshold), LOWLINE is pulled to V
cess to the unregulated supply is unavailable,
use LOWLINE to provide a nonmaskable in-
terrupt (NMI) to the P as shown in Figure 9a.
POWER-FAIL COMPARATOR
The power-fail comparator is an uncommitted
comparator that has no effect on the other func-
tions of the SP791. Common uses include moni-
toring supplies other than 5V (see the Typical
Operating Circuit and the Monitoring a Nega-
tive Voltage section) and early power-fail de-
tection when the unregulated power is easily ac-
cessible as shown in Figure 9b.
SP791DS/08
Figure 9. a) If the unregulated supply is inaccessible, LOWLINE generates the NMI for the P.
b) Use PFO to generate the P NMI if the unregulated supply is accessible.
UNREGULATED
SUPPLY
SP791 Low Power Microprocessor Supervisory with Battery Switch-Over
b.)
REGULATED
SUPPLY
FROM
REGULATOR
VOLTAGE
a.)
0.1 F
OUT
0.1 F
CC
. If ac-
with a
3
Vcc
7
3
Vcc
PFI
GND
Corporation
LOWLINE
GND
12
V
RESET
V
Corporation
4
BATT
OUT
WDI
V
RESET
V
4
BATT
OUT
WDI
PFO
POWER-FAIL INPUT
The Power-Fail Input (PFI) has a guaranteed
input leakage of +/-25nA max over temperature.
The typical comparator delay is 15 s from V
to V
V
ground if not used.
POWER-FAIL OUTPUT
The Power-Fail Output (PFO) goes low when
PFI falls below 1.25V. It sinks 3.2mA with a
saturation voltage of 0.1V. With PFI above
1.25V, PFO is actively pulled to V
necting PFI through a voltage divider to an un-
regulated supply allows PFO to generate an NMI
as the unregulated power begins to fall (see
Figure 9b).
15
10
2
1
11
OH
15
2
1
11
6
OL
(power being restored). Connect PFI to
0.1 F
3.0V
(power failing), and 55 s from V
0.1 F
3.0V
RESET
I/O LINE
POWER TO
CMOS RAM
NMI
P POWER
I/O LINE
POWER TO
CMOS RAM
RESET
NMI
P POWER
P
P
© Copyright 2000 Sipex Corporation
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