LMC555CMM National Semiconductor, LMC555CMM Datasheet - Page 6

• Manufacturer Part Number: LMC555CMM
• Description: Timer IC
• Manufacturer: National Semiconductor

Specifications of LMC555CMM

• Frequency: 3MHz
• No. Of Pins: 8
• Peak Reflow Compatible (260 C): No
• Supply Voltage: 15V
• Current Rating: 150A
• Leaded Process Compatible: No
• Mounting Type: Surface Mount
• Timer Type: Timer
• Package / Case: 8-MSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-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
= 3.9k
= 9k
= 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
= Ln2 (R
t
2
2
= Ln2 (R
= Ln2 (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
PULSE POSITION MODULATOR
This application uses the timer connected for astable opera-
tion, as in Figure 10 , with a modulating signal again applied
to the control voltage terminal. The pulse position varies with
CC
CC
A
A
= 9.1 k
= 9.1 k
= 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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