LM809M3-2.93 National Semiconductor, LM809M3-2.93 Datasheet - Page 6

• Manufacturer Part Number: LM809M3-2.93
• Description: IC, MPU RESET CKT, 15µA, 5.5V, 3-SOT-23
• Manufacturer: National Semiconductor

Specifications of LM809M3-2.93

• Threshold Voltage: 2.93V
• No. Of Supervisors / Monitors: 1
• Supply Voltage Range: 1.2V To 5.5V
• Reset Type: Active-Low
• Supply Current: 15µA
• Delay Time: 240ms
• Digital Ic Case Style: SOT-23
• Number Of Elements: 1
• Monitored Voltage 1 (typ): 3/3.3/5V
• Threshold Voltage 1 (max): 2.96V
• Battery Backup Switching: No
• Watchdog Timer: No
• Chip Enable Signals: No
• Reset Active Time: 840ms
• Manual Reset: No
• Package Type: SOT-23
• Operating Supply Voltage (min): 1V
• Operating Supply Voltage (max): 5.5V
• Reset Threshold Voltage (max): 2.96V
• Reset Threshold Voltage (min): 2.89V
• Family Name: LM809
• Power Dissipation: 320mW
• Operating Temp Range: -40C to 105C
• Operating Temperature Classification: Industrial
• Power Fail Detection: No
• Mounting: Surface Mount
• Pin Count: 3
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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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 volt-
ages.
Ensuring a Valid Reset Output Down to V
When V
longer sinks current. A high-impedance CMOS logic input
connected to RESET can therefore drift to undetermined
voltages. To prevent this situation, a 100kΩ resistor should
be connected from the RESET output to ground, as shown in
Figure 1.
A 100kΩ pull-up resistor to V
LM810, if RESET is required to remain valid for V
Negative-Going V
The
negative-going transients or glitches on V
the maximum pulse width a negative-going V
can have without causing a reset pulse. In general, as the
magnitude of the transient increases, going further below the
threshold, the maximum allowable pulse width decreases.
TABLE 1. Reset Thresholds Related to Common
FIGURE 1. RESET Valid to V
Threshold
4.63
4.38
4.00
3.08
2.93
2.63
2.45
LM809/810
Reset
CC
±
±
±
±
±
±
±
falls below 1V, the LM809 RESET output no
3%
3%
3%
3%
3%
3%
3%
CC
85 - 90%
79 - 84%
are
Supply Voltages
Transients
3.0V
relatively
CC
is also recommended for the
90 - 95%
86 - 90%
77 - 81%
72 - 76%
CC
3.3V
10105710
= Ground Circuit
immune
CC
. Figure 2 shows
CC
90 - 95%
85 - 90%
78 - 82%
CC
= 0V
5.0V
to
CC
transient
<
short
1V.
6
Typically, for the 4.63V and 4.38V version of the LM809/810,
a V
and lasts 20µs or less will not cause a reset pulse. A 0.1 µF
bypass capacitor mounted as close as possible to the V
pin will provide additional transient rejection.
Interfacing to µPs with Bidirectional Reset Pins
Microprocessors with bidirectional reset pins, such as the
Motorola 68HC11 series, can be connected to the LM809
RESET output. To ensure a correct output on the LM809
even when the microprocessor reset pin is in the opposite
state, connect a 4.7kΩ resistor between the LM809 RESET
output and the µP reset pin, as shown in Figure 3. Buffer the
LM809 RESET output to other system components.
LLP Mounting
The LLP package requires special mounting techniques
which are detailed in National Semiconductor Application
Note AN-1187. Referring to the section PCB Design Recom-
mendations, it should be noted that the pad style which
should be used with the LLP package is the NSMD (non-
solder mask defined) type.
CC
FIGURE 2. Maximum Transient Duration without
FIGURE 3. Interfacing to Microprocessors with
Causing a Reset Pulse vs. Reset Comparator
transient that goes 100mV below the reset threshold
Bidirectional Reset I/O
Overdrive
10105709
10105711
CC