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

14

Switchover at V

backup mode is entered before V

close to the 2.0V minimum required to reliably

retain data in CMOS RAM. Switchover at higher

V

life. When V

until V

to ensure a stable supply. V

V

Using a High Capacity Capacitor as a

Backup Power Source

Figure 21 shows two ways to use a High Value

Capacitor as a backup power source. The High

Value Capacitor may be connected through a

diode to the 3V input as in Figure 21A or, if a

5V supply is also available, the High Value

Capacitor may be charged up to the 5V supply

as in Figure 21B allowing a longer backup

period. Since V

is above the reset threshold, there are no

special precautions when using these

µP

supervisors with a High Value Capacitor.

Operation Without a Backup Power

Source

These

µP supervisors were designed for

battery-backed applications. If a backup power

source is not used, connect both VBATTERY

and V

Since there is no need to

switch over to any backup power source, V

OUT

does not need to be switched. A direct connec-

tion to V

the switch which may push V

Replacing the Backup Battery

If V

to ground, the backup battery can be removed

while V

triggering RESET/RESET. As long as V

CC

stays above V

be entered.

Adding Hysteresis to the Power-Fail

Comparator

The power-fail comparator has a typical input

hysteresis of 10mV. This is sufficient for most

applications where a power-supply line is being

monitored through an external voltage divider

(refer to the Monitoring an Additional Power

Supply section).

If additional noise margin is desired, connect a

resistor between PFO and PFI as shown in

Figure 22A. Select the ratio of R1 and R2 such

that PFI sees 1.25V when V

point (V

typically be more than 10 times the value of R1

or R2. The hysteresis window extends both

above (V

point (V

3.0V or 3.3V

GND

CONNECT TO

STATIC RAM

TO

µP

0.1F

CONNECT

pin 7*

1N4148

3.0V or 3.3V

GND

RESET for the SP690T/S/R and the SP802T/S/R

RESET for the SP804T/S/R and the SP805T/S/R

*

CONNECT TO

STATIC RAM

TO

µP

0.1F

CONNECT

pin 7*

1N4148

+5V

Figure 21. Using a High Capacity Capacitor as a Backup Power Source

A)

B)