SP703 Datasheet, PDF (9/16 Pages) Sipex Corporation – Low Power Microprocessor Supervisory with Battery Switch-Over

FEATURES
The SP703/704 devices provide four key func-
tions:
1. A battery backup switching 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 manual reset has been
pulled below 0.8V for at least 150ns.
4. A 1.25V threshold detector for power-fail
warning, low battery detection, or to monitor a
power supply other than +5V.
The SP703/704 devices differ only in their
supply voltage monitor level. The SP703
generates a reset when V_CC drops below 4.65V
while the SP704 generates a reset below 4.4V.
The SP703/704 devices are ideally suited for
applications in automotive systems, intelligent
instruments, and battery-powered computers and
controllers. All designs into an environment
where it is critical to monitor the power supply
to the µP and its related digital components will
find the SP703/704 ideal.
THEORY OF OPERATION
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
SP703/704 assert reset during power-up and
prevent code execution errors during power-
down or brownout conditions.
On power-up, once V_CC reaches 1V, RESET is
guaranteed to be a logic low. As V_CC rises,
RESET remains low. When V_CC exceeds the
reset threshold, RESET will remain low for
200ms, Figure 9. If a brownout condition
occurs and V_CC dips below the reset threshold,
RESET is triggered. Each time RESET is trig-
gered, it stays low for the reset pulse width
interval. If a brownout condition interrupts a
previously initiated reset pulse, the reset pulse
continues for another 200ms. On power-down,
once V_CC goes below the threshold, RESET is
guaranteed to be logic low until V_CC drops
below 1V. RESET is also triggered by a
manual reset
Regulated +5V
VCC
0.1µF
µP ^{RESET RESET}
NMI
PFO
MR
GND
VOUT
BUS _Pushbutton
Switch
CMOS VCC
RAM
GND
Unregulated
DC
VCC
R1
PFI
R2
VBATT
GND
3.6V
Lithium
Battery
Figure 8. Typical Operating Circuit
SP703/704DS/07
SP703/704 Low Power Microprocessor Supervisory
9
© Copyright 2000 Sipex Corporation