LM809, LM810

SNVS052D – SEPTEMBER 1999 – REVISED MAY 2013

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APPLICATIONS INFORMATION

Benefits of Precision Reset Thresholds

A microprocessor supply supervisor must provide a reset output within a predictable range of the supply voltage.

A common threshold range is between 5% and 10% below the nominal supply voltage. The 4.63V and 3.08V

options of the LM809/810 use highly accurate circuitry to ensure that the reset threshold occurs only within this

range (for 5V and 3.3V supplies). The other voltage options have the same tight tolerance to ensure a reset

signal for other narrow monitor ranges. See Table 1 for examples of how the standard reset thresholds apply to

3V, 3.3V, and 5V nominal supply voltages.

Table 1. Reset Thresholds Related to Common Supply Voltages

Reset Threshold

3.0V

3.3V

5.0V

4.63 ± 3%

90 - 95%

4.38 ± 3%

85 - 90%

4.00 ± 3%

78 - 82%

3.08 ± 3%

90 - 95%

2.93 ± 3%

86 - 90%

2.63 ± 3%

85 - 90%

77 - 81%

2.45 ± 3%

79 - 84%

72 - 76%

input connected to RESET can therefore drift to undetermined voltages. To prevent this situation, a 100k

Ω

resistor should be connected from the RESET output to ground, as shown in Figure 9.

A 100k

< 1V.

magnitude of the transient increases, going further below the threshold, the maximum allowable pulse width

the reset threshold and lasts 20µs or less will not cause a reset pulse. A 0.1 µF bypass capacitor mounted as

6

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