SP690T/S/R JAN 30-06 SP690T/S/R, 802/T/S/R, 804T/S/R, 805T/S/R Low Power Microprocessor Supervisory © 2006 Sipex Corporation
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THEORY OF OPERATION
The SP690T/S/R, SP802T/S/R, SP804T/S/R
and SP805T/S/R devices are microprocessor
(µP) supervisory circuits that monitor the power
supplied to digital circuits such as microproces-
sors, microcontrollers, or memory. The series is
an ideal solution for portable, battery-powered
equipment that requires power supply monitoring.
Implementing this series will reduce the
number of components and overall complexity.
The watchdog functions of this product family
will continuously oversee the operational status
of a system.
These µP supervisory circuits are not short-
circuit protected. Shorting V
OUT
to ground -
excluding power-up transients such as charging
a decoupling capacitor - may potentially damage
these devices. Decouple both V
CC
and V
BATTERY
pins to ground by placing 0.1µF capacitors as
close to the device as possible. The operational
features and benefits of the SP690T/S/R,
SP802T/S/R, SP804T/S/R and SP805T/S/R
devices are described in more detail below.
Reset Output
The microprocessor's (µP's) reset input starts
the µP in a known state. When the µP is in an
unknown state, it should be held in reset. The
SP690T/S/R, SP802T/S/R, SP804T/S/R and
SP805T/S/R devices assert reset during
power-up and prevent code execution errors
during power-down or brownout conditions.
RESET is guaranteed to be a logic LOW for 0V
< V
CC
< V
RST
, provided that V
BATTERY
is greater
than 1V. Without a backup battery, RESET is
guaranteed valid for V
CC
> 1V. Once V
CC
exceeds the reset threshold, an internal timer
keeps RESET low for the reset timeout period.
After this period, RESET goes HIGH, as seen in
Figure 19.
If a brownout condition occurs and V
CC
dips
below the reset threshold, RESET goes LOW.
Each time RESET is triggered, it stays low for
the reset timeout period. Any time V
CC
goes
below the reset threshold, the internal timer
restarts.
FEATURES
The SP690T/S/R, SP802T/S/R, SP804T/S/R
and SP805T/S/R devices provide four key
functions:
1. A battery backup switch for CMOS RAM,
CMOS microprocessors, or other logic.
2. A reset output during power-up, power-down
and brownout conditions.
3. A reset pulse if the optional watchdog timer
has not been toggled within a specified time.
4. A 1.25V threshold detector for power-fail
warning, low battery detection, or to monitor a
power supply other than 3.3V or 3.0V.
The SP690T/S/R, SP802T/S/R, SP804T/S/R
and SP805T/S/R devices differ in their reset-
voltage threshold levels and are ideally suited
for applications in automotive systems, intelligent
instruments, and battery-powered computers and
controllers. The series is a solid match for
designs where it is critical to monitor the
power supply to the µP and it’s related digital
components.
Figure 20. Typical Operating Circuit
GND
GND
RESET
NMI
I/O LINE
V
CC
pin 7*
PFO
WDI
V
OUT
BUS
V
CC
GND
V
BATTERY
R
2
R
1
Unregulated
Regulated +3.3V or +3.0V
V
CC
0.1µF
PFI
DC
Lithium
Battery
3.6V
µP
CMOS
RAM
0.1µF
RESET for the SP690T/S/R and the SP802T/S/R
RESET for the SP804T/S/R and the SP805T/S/R
*
SP690T/S/R
SP802T/S/R
SP804T/S/R
SP805T/S/R
