13

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

The watchdog timer can also initiate a reset.

Refer to the Watchdog Input section.

The SP804T/S/R and SP805T/S/R active-HIGH

RESET output is open drain and the inverse

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

outputs.

RESET is also triggered by a watchdog timeout.

If WDI remains either high or low for a period

that exceeds the watchdog timeout period (1.6

sec), RESET pulses low for 200mS. As long as

RESET is asserted, the watchdog timer remains

cleared. When RESET comes high, the watch-

dog resumes timing and must be serviced within

1.6sec. If WDI is tied high or low, a RESET

pulse is triggered every 1.8sec (t

Reset Threshold

The SP690T and SP805T devices are designed

for 3.3V systems with a

±5% power-supply

tolerance and a 10% system tolerance. Except

for watchdog faults, reset will not assert as long

as the power supply remains above 3.15V (3.3V

- 5%). Reset is guaranteed to assert before the

power supply falls below 3.0V.

The SP690S and SP805S devices are designed

for 3.3V

±10% power supplies. Except for

watchdog faults, they are guaranteed not to

assert reset as long as the supply remains above

3.0V (3.3V - 10%). Reset is guaranteed to

assert before the power supply fails below 2.85V

(V

The SP690R and SP805R devices are optimized

for monitoring 3.0V

±10%powersupplies. Reset

will not occur until V

- 10%), but is guaranteed to occur before the

supply falls below 2.55V (3.0V - 15%).

The SP802T/S/R and SP804T/S/R devices are

respectively similar to the SP690T/S/R and

SP805T/S/R devices with tightened reset

and power-fail threshold tolerances.

Watchdog Input

The watchdog circuit monitors the

µP's activity.

If the

µP does not toggle the watchdog input

(WDI) within 1.6sec, a reset pulse is triggered.

The internal 1.6sec timer is cleared by either a

reset pulse or by a transition (LOW-to-HIGH or

HIGH-to-LOW) at WDI. If WDI is tied HIGH

or LOW, a RESET pulse is triggered every

1.8sec (t

As long as reset is asserted, the timer remains

cleared and does not count. As soon as reset is

de-asserted, the timer starts counting. Unlike

the 5V SP690A series, the watchdog function

cannot be disabled.

Power-Fail Comparator

The power-fail comparator can be used as an

under-voltage detector to signal the failing of a

power supply (it is completely separate from the

rest of the circuitry and does not need to be

dedicated to this function). The PFI input is

compared to an internal 1.25V. If PFI is less than

V

The power-fail comparator turns off and PFO

goes LOW when V

power-down. The power-fail comparator turns

on as V

comparator is not used, connect PFI to ground

and leave PFO unconnected.

Backup-Battery Switchover

In the event of a brownout or power failure, it

may be necessary to preserve the contents of

RAM. With a backup battery installed at

V

RAM to backup power when V

This family of

µP supervisors (designed for

3.3V and 3V systems) doesn't always connect

V

than V

a 15

Ω switch) when V

V