SP791CN SIPEX [Sipex Corporation], SP791CN Datasheet - Page 8

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

Figure 2. Manual-Reset Timing Diagram
SP791DS/08
FEATURES
The SP791 is a microprocessor ( P) supervi-
sory circuit that monitors the power supplied to
digital circuits such as microprocessors,
microcontrollers, or memory. The SP791 is an
ideal solution for portable, battery-powered
equipment that require power supply monitor-
ing. The SP791 watchdog functions will con-
tinuously oversee the operational status of a sys-
tem. Implementing the SP791 will reduce the
number of components and overall complexity
in a design that requires power supply monitor-
ing circuitry. The operational features and ben-
efits of the SP791 are described in more detail
below.
THEORY OF OPERATION
The SP791 is a complete P supervisor IC and
provides the following main functions:
Typical Operating Circuit
1) P reset
CE
RESET
CE
OUT
power fluctuations such as power-up, power-
down, and brown out conditions, and is guar-
anteed to be in the correct state for V
to 1V.
MR
0V
IN
UNREGULATED
RESET output is asserted during
SUPPLY
RESET SOURCES
OTHER SYSTEM
SP791 Low Power Microprocessor Supervisory with Battery Switch-Over
SUPPLY FAILURE
UNREGULATED
+5V
0.1 F
25 s MIN
0.47F
7 s TYP
15 s TYP
CC
down
V
V
MR
PFI
PFO
cc
BATT
GND
BATT
Corporation
ON
LOWLINE
8
RESET
CE
CE
V
WDO
SWT
WDI
OUT
OUT
Figure 3. Diode "OR" connections allow multiple reset
MANUAL RESET INPUT
Many microprocessor or microcontroller prod-
ucts include manual-reset capability, allowing
the operator or test technician to initiate a reset.
The Manual Reset Input (MR) can be connected
directly to a switch, without an external pull-up
resistor. It connects to a 1.25V comparator, and
has an internal pull-up to V
ure 1. The propagation delay from asserting MR
to RESET being asserted is 7us typical. Pulsing
IN
sources to connect to MR.
3) Power Fail Comparator
5) Internal switch
2) Manual-Reset input
SOURCES
4) Watchdog function
OTHER
RESET
ADDRESS
DECODE
RESET output
fail warning and low-battery detection, or
monitors another power supply.
where the watchdog output goes to a logic
LOW state if the watchdog input is not toggled
for a period greater than the timeout period.
V
old and below V
*
MANUAL RESET
DIODES NOT REQUIRED ON OPEN-DRAIN OUTPUTS
BATT
0.1 F
if the V
AO-A15
RESET
I/O
NMI
INT
P
CC
*
*
CMOS
RAM
BATT
falls below the reset thresh-
Switches over from V
© Copyright 2000 Sipex Corporation
.
OUT
Manually resets
Monitors P activity
Provides for power-
as shown in Fig-
MR
Corporation
CC
to