SGM811-RXKA4SLASHTR datasheet(8/12 Pages) SGMICRO

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Microprocessor Supervisory

with Manual Reset Input

SGM811/812

APPLICATION INFORMATION

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 100ns and to accept inputs longer in

duration than 10μs.

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

VCC

Figure 1. Ensuring a Valid RESET Output Down to VCC = 0V

Ensuring A Valid Reset Output Down to Vcc

= 0V

When VCC falls below 1.0 V, the SGM811/SGM812’s 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 100kΩ resistor should be

connected from RESET to ground.

Reset Output

On power-up and after VCC rises above the reset threshold, an

internal timer holds the reset output active for 240ms (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 240ms (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 remains valid

(low) with VCC as low as 1V. This ensures that 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

VCC

VREF

t1 = RESET Time = 240ms Typical

VREF = RESET Voltage Threshold

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 reset output, which is directly proportional to VCC (this is

guaranteed only while VCC is greater than 1V). This enables the

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

within the minimum and maximum specifications for VCC.

SG Micro Corp

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