LMC555CN National Semiconductor, LMC555CN Datasheet - Page 6

• Manufacturer Part Number: LMC555CN
• Description: IC, TIMER CMOS, DIP8, 555
• Manufacturer: National Semiconductor

Specifications of LMC555CN

• Operating Mode: Astable / Monostable
• No. Of Timers: 1
• Clock External Input: No
• Supply Voltage Range: 1.5V To 12V
• Digital Ic Case Style: DIP
• No. Of Pins: 8
• Operating Temperature Range: -40°C
• Frequency: 3MHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Application Info
V
TIME = 20 µs/Div.
R
R
C = 0.01µF
The charge time (output high) is given by
And the discharge time (output low) by:
Thus the total period is:
The frequency of oscillation is:
Figure 6 may be used for quick determination of these RC
Values. The duty cycle, as a fraction of total period that the
output is low, is:
FREQUENCY DIVIDER
The monostable circuit of Figure 1 can be used as a fre-
quency divider by adjusting the length of the timing cycle.
Figure 7 shows the waveforms generated in a divide by three
circuit.
CC
A
B
= 3.9kΩ
= 9kΩ
= 5V
FIGURE 6. Free Running Frequency
FIGURE 5. Astable Waveforms
T = t
Top Trace: Output 5V/Div.
Bottom Trace: Capacitor Voltage 1V/Div.
t
1
1
+ t
= 0.693 (R
t
2
2
= 0.693 (R
= 0.693 (R
(Continued)
A
+ R
B
)C
A
B
+ R
)C
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B
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)C
6
V
TIME = 20 µs/Div. Middle Trace: Output 2V/Div.
R
C = 0.01µF
PULSE WIDTH MODULATOR
When the timer is connected in the monostable mode and
triggered with a continuous pulse train, the output pulse
width can be modulated by a signal applied to the Control
Voltage Terminal. Figure 8 shows the circuit, and in Figure 9
are some waveform examples.
V
TIME = 0.2 ms/Div. Bottom Trace: Output Voltage 2V/Div.
R
C = 0.01µF
CC
CC
A
A
= 9.1 kΩ
= 9.1 kΩ
= 5V
= 5V
FIGURE 9. Pulse Width Modulator Waveforms
FIGURE 7. Frequency Divider Waveforms
FIGURE 8. Pulse Width Modulator
Top Trace: Input 4V/Div.
Bottom Trace: Capacitor 2V/Div.
Top Trace: Modulation 1V/Div.
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