SGM811/812

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APPLICATION NOTES

MANUAL RESET

The SGM811/SGM812 is equipped with a manual reset input

This input is designed to operate in a noisy environment

where unwanted glitches could be induced. These glitches

could be produced by the bouncing action of a switch contact,

or where a manual reset switch may be located some distance

away from the circuit (the cabling of which may pick-up

noise).

The manual reset input is guaranteed to ignore logically valid

inputs that are faster than 100 ns and to accept inputs longer in

duration than 10 µs.

BENEFITS OF A VERY ACCURATE RESET THRESHOLD

Because the SGM811/SGM812 can operate effectively even

when there are large degradations of the supply voltages, the

possibility of a malfunction during a power failure is greatly

reduced. Another advantage of the SGM811/SGM812 is its

very accurate internal voltage reference circuit. Combined,

these

benefits

produce

an

exceptionally

reliable

microprocessor supervisory circuit.

SGM811

GND

RESET

Figure 1. Ensuring a Valid

RESET no

longer sinks current. Therefore, a high impedance CMOS logic

input connected to

RESET may drift to undetermined logic

levels. To eliminate this problem, a 100 k Ω resistor should be

connected from

RESET to ground.

RESET OUTPUT

internal timer holds the reset output active for 240 ms (typical).

This is intended as a power-on reset signal for the processor. It

allows time for both the power supply and the microprocessor

to stabilize after power-up. If a power supply brownout or

interruption occurs, the reset output is similarly activated and

remains active for 240 ms (typical) after the supply recovers.

This allows time for the power supply and microprocessor to

stabilize.

The SGM811 provides an active low reset output (

RESET )

while the SGM812 provides an active high output (

RESET ).

During power-down of the SGM811, the

RESET output

the microprocessor is held in a stable shutdown condition as

the supply falls and also ensures that no spurious activity can

occur via the microprocessor as it powers up.

Glitch Immunity

The SGM811/SGM812 contains internal filtering circuitry

providing glitch immunity from fast transient glitches on the

power supply line.

RESET

Figure 2. Power Fail

RESET Timing

INTERFACING TO OTHER DEVICES

Output

The SGM811/SGM812 is designed to integrate with as many

devices as possible. One feature of the SGM811/SGM812 is the

the part to be used with both 3 V and 5 V, or any nominal

voltage within the minimum and maximum specifications for