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Precision Timer
NE555
Connection Diagram
SO-8 NE555M
RESET
FUNCTION TABLE
TRIGGER VOLTAGE
THRESHOLD VOLTAGE
OUTPUT
DISCHARGE SWITCH
Low
Irrelevant
Irrelevant High
>2/3VDD
Low
High Low
On
High High
<1/3VDD
>1/3V DD
>1/3VDD
Off On
High
<2/3V DD
As previously established
DIP-8 NE555N
General Description
The NE555 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 oscillator, 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 200mA or drive TTL circuits.
Features
n n n n n n Direct replacement for SE555/NE555 Timing from microseconds through hours Operates in both astable and monostable modes Adjustable duty cycle Output can source or sink 200 mA Output and supply TTL compatible
n Normally on and normally off output
Applications
n n n n n n n Precision timing Pulse generation Sequential timing Time delay generation Pulse width modulation Pulse position modulation Linear ramp generator
Wing Shing Computer Components Co., (H.K.)Ltd. Homepage: http://www.wingshing.com
Tel:(852)2341 9276 Fax:(852)2797 8153 E-mail: wsccltd@hkstar.com
1
NE555
ELECTRICAL CHARACTERISTICS
(TA = 25C, VCC = +5V to +15V, unless othewise specified) Parameter Conditions Min Supply Voltage Supply Current
Note 4
Limits Typ 3 10 2 1 Max 16 6 15 5
Units
4.5 VCC VCC Vcc=5V,No load OUTPUT HIGH = 5V, RL = OUTPUT LOW = 15V, RL = OUTPUT LOW
V mA
Timing Error, Monostable Initial Accuracy Drift with Temperature Accuracy over Temperature Drift with Supply Timing Error, Astable Initial Accuracy Drift with Temperature Accuracy over Temperature Drift with Supply Threshold Voltage Trigger Voltage Trigger Current Reset Voltage Reset Current Threshold Current Control Voltage Level Pin 7 Leakage Output High Pin 7 Sat (Note 7) Output Low Output Low VCC = 15V, I7 = 15mA VCC = 4.5V, I7 = 4.5mA 180 80 200 mV mV
Reset at Vcc
3
% ppm/C %
RA = 1k to 100k, C = 0.1F, (Note 5)
50 1.5 0.1 2.25
0.5
%/V % ppm/C % %/V x VCC
RA, RB = 1k to 100k, C = 0.1F, (Note 5)
150 3.0 0.30 0.667
VCC = 15V VCC = 5V Trigger at 0V
4.5 1.1
5 1.67 0.5
0.7
5.6 2.2
2
1
V V
uA
0.3
V
(Note 6) VCC = 15V VCC = 5V 9 2.6
0.1 30 10 3.33 20 1
0.4 250 11 4 100
mA
nA
V nA
2
NE555
Electrical Characteristics (Notes 1, 2)
Parameter
(Continued)
(TA = 25C, VCC = +5V to +15V, unless othewise specified) Conditions Min Output Voltage Drop (Low) VCC = 15V ISINK = 10mA ISINK = 50mA ISINK = 100mA ISINK = 200mA VCC = 5V ISINK = 8mA ISINK = 5mA Output Voltage Drop (High) ISOURCE = 200mA, VCC = 15V ISOURCE = 100mA, VCC = 15V VCC = 5V Rise Time of Output Fall Time of Output
Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. Note 3: For operating at elevated temperatures the device must be derated above 25C based on a +150C maximum junction temperature and a thermal resistance 170C/W (S0-8), junction to ambient. Note 4: Supply current when output high typically 9mA and MAX. is 13mA at Vcc=15V. Note 5: Tested at VCC = 5V and VCC = 15V. .
Limits Typ 0.1 0.4 2 2.5
0.15 0.4
Units Max 0.25 0.75 2.5 V V V V V V V V V
300 300
0.1 0.25
0.35
12.5 12.75 2.75 13.3 3.3 100 100
ns ns
Note 6: This will determine the maximum value of RA + RB for 15V operation. The maximum total (RA + RB) is 20M. Note 7: No protection against excessive pin 7 current is necessary providing the package dissipation rating will not be exceeded.
RECOMMENDED OPERATING CONDITIONS
MIN 4.5 MAX. 16 V Input voltage (control,reset,threshold, and trigger ) Output current Operating free-air temperature, TA
0
+ -
UNIT
Supply voltage ,Vcc
Vcc
200
mA
o
70 0
C
3
NE555
Applications Information
MONOSTABLE OPERATION In this mode of operation, the timer functions as a one-shot (Figure 1). The external capacitor is initially held discharged by a transistor inside the timer. Upon application of a negative trigger pulse of less than 1/3 VCC to pin 2, the flip-flop is set which both releases the short circuit across the capacitor and drives the output high. NOTE: In monostable operation, the trigger should be driven high before the end of timing cycle.
FIGURE 3. Time Delay ASTABLE OPERATION If the circuit is connected as shown in Figure 4 (pins 2 and 6 connected) it will trigger itself and free run as a multivibrator. The external capacitor charges through RA + RB and discharges through RB. Thus the duty cycle may be precisely set by the ratio of these two resistors.
FIGURE 1. Monostable The voltage across the capacitor then increases exponentially for a period of t = 1.1 RA C, at the end of which time the voltage equals 2/3 VCC. The comparator then resets the flip-flop which in turn discharges the capacitor and drives the output to its low state. Figure 2 shows the waveforms generated in this mode of operation. Since the charge and the threshold level of the comparator are both directly proportional to supply voltage, the timing internal is independent of supply.
FIGURE 4. Astable In this mode of operation, the capacitor charges and discharges between 1/3 VCC and 2/3 VCC. As in the triggered mode, the charge and discharge times, and therefore the frequency are independent of the supply voltage.
VCC = 5V TIME = 0.1 ms/DIV. RA = 9.1k C = 0.01F
Top Trace: Input 5V/Div. Middle Trace: Output 5V/Div. Bottom Trace: Capacitor Voltage 2V/Div.
FIGURE 2. Monostable Waveforms During the timing cycle when the output is high, the further application of a trigger pulse will not effect the circuit so long as the trigger input is returned high at least 10s before the end of the timing interval. However the circuit can be reset during this time by the application of a negative pulse to the reset terminal (pin 4). The output will then remain in the low state until a trigger pulse is again applied. When the reset function is not in use, it is recommended that it be connected to VCC to avoid any possibility of false triggering.
Figure 3 is a nomograph for easy determination of R, C values for various time delays.
4
NE555
Physical Dimensions
inches (millimeters) unless otherwise noted
NE555M
Pad locatin
DISCHARGE CONTROL VOLTAGE THRESHOLD
7
6
5
Vcc
8
4
RESET
GND
1
95
95
TRIGGER
2
3
OUTPUT Chip Size: 1.02x 1.07 mm
Pad N 1 2 3 4 5 6 7 8
Pad Name GND TRIGGER OUTPUT RESET THRESHOLD CONTROL VOLTAGE DISCHARGE Vcc
Coordinates mkm X Y 95 313 115 126 590 810 810 780 420 125 126 451 635 829 893 492
5

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