PDF LM555C Fiche technique - National Semiconductor

Numéro de référence LM555C
Description Timer
Fabricant National Semiconductor 
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LM555C Datasheet, Description
February 1995
LM555 LM555C Timer
General Description
The LM555 is a highly stable device for generating accurate
time delays or oscillation Additional terminals are provided
for triggering or resetting if desired In the time delay mode
of operation the time is precisely controlled by one external
resistor and capacitor For astable operation as an oscilla-
tor the free running frequency and duty cycle are accurately
controlled with two external resistors and one capacitor
The circuit may be triggered and reset on falling waveforms
and the output circuit can source or sink up to 200 mA or
drive TTL circuits
Y Direct replacement for SE555 NE555
Y Timing from microseconds through hours
Y Operates in both astable and monostable modes
Y Adjustable duty cycle
Y Output can source or sink 200 mA
Y Output and supply TTL compatible
Y Temperature stability better than 0 005% per C
Y Normally on and normally off output
Y Precision timing
Y Pulse generation
Y Sequential timing
Y Time delay generation
Y Pulse width modulation
Y Pulse position modulation
Y Linear ramp generator
Schematic Diagram
C1995 National Semiconductor Corporation TL H 7851
TL H 7851 – 1
RRD-B30M115 Printed in U S A
LM555C Fiche technique
Electrical Characteristics TA e 25 C VCC e a5V to a15V (unless othewise specified) (Continued)
Min Typ Max Min Typ Max
Output Voltage Drop (Low)
VCC e 15V
ISINK e 10 mA
ISINK e 50 mA
ISINK e 100 mA
ISINK e 200 mA
VCC e 5V
ISINK e 8 mA
ISINK e 5 mA
0 1 0 15
04 05
2 22
0 1 0 25
0 1 0 25
0 4 0 75
2 25
0 25 0 35
Output Voltage Drop (High) ISOURCE e 200 mA VCC e 15V
12 5
ISOURCE e 100 mA VCC e 15V 13 13 3
VCC e 5V
3 33
12 75
2 75
12 5
13 3
Rise Time of Output
100 100
Fall Time of Output
100 100 ns
Note 1 For operating at elevated temperatures the device must be derated above 25 C based on a a150 C maximum junction temperature and a thermal
resistance of 164 c w (T0-5) 106 c w (DIP) and 170 c w (S0-8) junction to ambient
Note 2 Supply current when output high typically 1 mA less at VCC e 5V
Note 3 Tested at VCC e 5V and VCC e 15V
Note 4 This will determine the maximum value of RA a RB for 15V operation The maximum total (RA a RB) is 20 MX
Note 5 No protection against excessive pin 7 current is necessary providing the package dissipation rating will not be exceeded
Note 6 Refer to RETS555X drawing of military LM555H and LM555J versions for specifications
Connection Diagrams
Metal Can Package
Dual-In-Line and Small Outline Packages
Top View
TL H 7851 – 2
Order Number LM555H or LM555CH
See NS Package Number H08C
Top View
TL H 7851 – 3
Order Number LM555J LM555CJ
LM555CM or LM555CN
See NS Package Number J08A M08A or N08E

3 Page

LM555C pdf
Applications Information (Continued)
Figure 5 shows the waveforms generated in this mode of
TL H 7851–9
VCC e 5V
Top Trace Output 5V Div
TIME e 20 ms DIV Bottom Trace Capacitor Voltage 1V Div
RA e 3 9 kX
RB e 3 kX
C e 0 01 mF
FIGURE 5 Astable Waveforms
The charge time (output high) is given by
t1 e 0 693 (RA a RB) C
And the discharge time (output low) by
t2 e 0 693 (RB) C
Thus the total period is
T e t1 a t2 e 0 693 (RA a2RB) C
The frequency of oscillation is
1 1 44
fe e
T (RA a 2 RB) C
Figure 6 may be used for quick determination of these RC
The duty cycle is
D e RB
RA a 2RB
VCC e 5V
Top Trace Input 4V Div
TIME e 20 ms DIV Middle Trace Output 2V Div
RA e 9 1 kX
C e 0 01 mF
Bottom Trace Capacitor 2V Div
FIGURE 7 Frequency Divider
TL H 7851 – 11
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 pin 5 Figure
8 shows the circuit and in Figure 9 are some waveform
TL H 7851 – 12
FIGURE 8 Pulse Width Modulator
TL H 7851–10
FIGURE 6 Free Running Frequency
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
TL H 7851 – 13
VCC e 5V
Top Trace Modulation 1V Div
TIME e 0 2 ms DIV Bottom Trace Output Voltage 2V Div
RA e 9 1 kX
C e 0 01 mF
FIGURE 9 Pulse Width 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 the modulating signal since the threshold voltage and
hence the time delay is varied Figure 11 shows the wave-
forms generated for a triangle wave modulation signal


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