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SGM812-RXKA4 Datasheet(PDF) 7 Page - SG Micro Corp |
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SGM812-RXKA4 Datasheet(HTML) 7 Page - SG Micro Corp |
7 / 9 page SGM811/812 7 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 VCC VCC Figure 1. Ensuring a Valid RESET Output Down to VCC = 0V ENSURING A VALID RESET OUTPUT DOWN TO VCC = 0 V When VCC falls below1.0 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 100 k Ω 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 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 remains valid (low) with VCC as low as 1 V. 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. t1 t1 RESET VCC VREF VREF VREF 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 1 V). This enables the part to be used with both 3 V and 5 V, or any nominal voltage within the minimum and maximum specifications for VCC. |
Similar Part No. - SGM812-RXKA4 |
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Similar Description - SGM812-RXKA4 |
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