www.fairchildsemi.com LM555 Single Timer Features Description • • • • • The LM555 is a highly stable controller capable of producing accurate timing pulses. With a monostable operation, the time delay is controlled by one external resistor and one capacitor. With an astable operation, the frequency and duty cycle are accurately controlled by two external resistors and one capacitor. High Current Drive Capability (200mA) Adjustable Duty Cycle Temperature Stability of 0.005%/C Timing From Sec to Hours Turn off Time Less Than 2Sec Applications • • • • 8-DIP Precision Timing Pulse Generation Time Delay Generation Sequential Timing 1 8-SOIC 1 Internal Block Diagram R GND 1 Trigger 2 R Comp. Output Reset 3 OutPut Stage R 8 Vcc 7 Discharge 6 Threshold 5 Control Voltage Discharging Tr. F/F 4 Vref Comp. Rev. 1.0.5 ©2012 Fairchild Semiconductor Corporation LM555 Absolute Maximum Ratings (TA = 25C) Parameter Symbol Value Unit VCC 16 V TLEAD 300 C PD 600 mW Operating Temperature Range (LM555) TOPR 0 ~ +70 C Storage Temperature Range TSTG -65 ~ +150 C Supply Voltage Lead Temperature (Soldering 10sec) Power Dissipation 2 LM555 Electrical Characteristics (TA = 25C, VCC = 5 ~ 15V, unless otherwise specified) Parameter Symbol Conditions Min. Typ. Max. Unit Supply Voltage VCC - 4.5 - 16 V Supply Current (Low Stable) (Note1) ICC VCC = 5V, RL = - 3 6 mA VCC = 15V, RL = - 7.5 15 mA - 1.0 50 0.1 3.0 % ppm/C %/V 2.25 150 0.3 - % ppm/C %/V Timing Error (Monostable) Initial Accuracy (Note2) Drift with Temperature (Note4) Drift with Supply Voltage (Note4) Timing Error (Astable) Intial Accuracy (Note2) Drift with Temperature (Note4) Drift with Supply Voltage (Note4) ACCUR t/T t/VCC ACCUR t/T t/VCC RA = 1k to100k C = 0.1F RA = 1k to 100k C = 0.1F VCC = 15V 9.0 10.0 11.0 V VCC = 5V 2.6 3.33 4.0 V VCC = 15V - 10.0 - V VCC = 5V - 3.33 - V - 0.1 0.25 A VCC = 5V 1.1 1.67 2.2 V VCC = 15V 4.5 5 5.6 V 0.01 2.0 A 0.7 1.0 V 0.1 0.4 mA Control Voltage VC Threshold Voltage VTH Threshold Current (Note3) ITH Trigger Voltage VTR Trigger Current ITR Reset Voltage VRST - Reset Current IRST - Low Output Voltage High Output Voltage VOL VOH - 0.5 - VTR = 0V 0.4 VCC = 15V ISINK = 10mA ISINK = 50mA - 0.06 0.3 0.25 0.75 V V VCC = 5V ISINK = 5mA - 0.05 0.35 V 12.5 13.3 - 12.75 V V 2.75 3.3 - V VCC = 15V ISOURCE = 200mA ISOURCE = 100mA VCC = 5V ISOURCE = 100mA Rise Time of Output (Note4) tR - - 100 - ns Fall Time of Output (Note4) tF - - 100 - ns Discharge Leakage Current ILKG - - 20 100 nA Notes: 1. When the output is high, the supply current is typically 1mA less than at VCC = 5V. 2. Tested at VCC = 5.0V and VCC = 15V. 3. This will determine the maximum value of RA + RB for 15V operation, the max. total R = 20M, and for 5V operation, the max. total R = 6.7M 4. These parameters, although guaranteed, are not 100% tested in production. 3 LM555 Application Information Table 1 below is the basic operating table of 555 timer: Table 1. Basic Operating Table Threshold Voltage Trigger Voltage Discharging Tr. Reset(PIN 4) Output(PIN 3) (Vth)(PIN 6) (Vtr)(PIN 2) (PIN 7) Don't care Don't care Low Low ON Vth > 2Vcc / 3 Vth > 2Vcc / 3 High Low ON Vcc / 3 < Vth < 2 Vcc / 3 Vcc / 3 < Vth < 2 Vcc / 3 High Vth < Vcc / 3 Vth < Vcc / 3 High High OFF When the low signal input is applied to the reset terminal, the timer output remains low regardless of the threshold voltage or the trigger voltage. Only when the high signal is applied to the reset terminal, the timer's output changes according to threshold voltage and trigger voltage. When the threshold voltage exceeds 2/3 of the supply voltage while the timer output is high, the timer's internal discharge Tr. turns on, lowering the threshold voltage to below 1/3 of the supply voltage. During this time, the timer output is maintained low. Later, if a low signal is applied to the trigger voltage so that it becomes 1/3 of the supply voltage, the timer's internal discharge Tr. turns off, increasing the threshold voltage and driving the timer output again at high. 1. Monostable Operation +Vcc 2 10 THRES 6 3 OUT C1 GND RL CONT 5 1 10 M 1M 10 0k R TRIG Capacitance(uF) 2 1 10 DISCH 7 10 k Trigger =1 k 8 Vcc A 4 RESET RA 0 10 -1 10 -2 10 C2 -3 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 10 1 10 Time Delay(s) Figure 1. Monostable Circuit Figure 3. Waveforms of Monostable Operation 4 Figure 2. Resistance and Capacitance vs. Time delay(td) 2 10 LM555 Figure 1 illustrates a monostable circuit. In this mode, the timer generates a fixed pulse whenever the trigger voltage falls below Vcc/3. When the trigger pulse voltage applied to the #2 pin falls below Vcc/3 while the timer output is low, the timer's internal flip-flop turns the discharging Tr. off and causes the timer output to become high by charging the external capacitor C1 and setting the flip-flop output at the same time. The voltage across the external capacitor C1, VC1 increases exponentially with the time constant t=RA*C and reaches 2Vcc/3 at td=1.1RA*C. Hence, capacitor C1 is charged through resistor RA. The greater the time constant RAC, the longer it takes for the VC1 to reach 2Vcc/3. In other words, the time constant RAC controls the output pulse width. When the applied voltage to the capacitor C1 reaches 2Vcc/3, the comparator on the trigger terminal resets the flip-flop, turning the discharging Tr. on. At this time, C1 begins to discharge and the timer output converts to low. In this way, the timer operating in the monostable repeats the above process. Figure 2 shows the time constant relationship based on RA and C. Figure 3 shows the general waveforms during the monostable operation. It must be noted that, for a normal operation, the trigger pulse voltage needs to maintain a minimum of Vcc/3 before the timer output turns low. That is, although the output remains unaffected even if a different trigger pulse is applied while the output is high, it may be affected and the waveform does not operate properly if the trigger pulse voltage at the end of the output pulse remains at below Vcc/3. Figure 4 shows such a timer output abnormality. Figure 4. Waveforms of Monostable Operation (abnormal) 2. Astable Operation +Vcc 100 RA Vcc 7 TRIG RL C1 GND OUT 0.1 M 10 3 1M RB THRES 6 1 0k 10 DISCH 2 Capacitance(uF) RESET (RA+2RB) 10 1k 8 k 10 4 0.01 CONT 5 1 C2 1E-3 100m 1 10 100 1k 10k 100k Frequency(Hz) Figure 5. Astable Circuit Figure 6. Capacitance and Resistance vs. Frequency 5 LM555 Figure 7. Waveforms of Astable Operation An astable timer operation is achieved by adding resistor RB to Figure 1 and configuring as shown on Figure 5. In the astable operation, the trigger terminal and the threshold terminal are connected so that a self-trigger is formed, operating as a multi vibrator. When the timer output is high, its internal discharging Tr. turns off and the VC1 increases by exponential function with the time constant (RA+RB)*C. When the VC1, or the threshold voltage, reaches 2Vcc/3, the comparator output on the trigger terminal becomes high, resetting the F/F and causing the timer output to become low. This in turn turns on the discharging Tr. and the C1 discharges through the discharging channel formed by RB and the discharging Tr. When the VC1 falls below Vcc/3, the comparator output on the trigger terminal becomes high and the timer output becomes high again. The discharging Tr. turns off and the VC1 rises again. In the above process, the section where the timer output is high is the time it takes for the VC1 to rise from Vcc/3 to 2Vcc/3, and the section where the timer output is low is the time it takes for the VC1 to drop from 2Vcc/3 to Vcc/3. When timer output is high, the equivalent circuit for charging capacitor C1 is as follows: RA RB Vcc C1 dv c1 V cc – V 0- C 1 ------------- = ------------------------------dt RA + RB V C1 0+ = V CC 3 Vc1(0-)=Vcc/3 1 2 t - – ------------------------------------ R + R C1 A B 2 V C1 t = V CC 1 – --- e 3 3 Since the duration of the timer output high state(tH) is the amount of time it takes for the VC1(t) to reach 2Vcc/3, 6 LM555 t H - – ------------------------------------ R A + R B C1 2 2 V C1 t = --- V CC = V 1 – --- e 3 3 CC 4 t H = C 1 R A + R B In2 = 0.693 R A + R B C 1 5 The equivalent circuit for discharging capacitor C1, when timer output is low is, as follows: RB C1 VC1(0-)=2Vcc/3 RD dv C1 1 C 1 -------------- + ----------------------- V C1 = 0 dt RA + RB 2 V C1 t = --- V 3 CC e 6 t - ------------------------------------ R A + R D C1 7 Since the duration of the timer output low state(tL) is the amount of time it takes for the VC1(t) to reach Vcc/3, t 1 2 --- V = --- V 3 CC 3 CC e L - ----------------------------------- R + R C1 A D 8 t L = C 1 R B + R D In2 = 0.693 R B + R D C 1 9 Since RD is normally RB>>RD although related to the size of discharging Tr., (10) tL=0.693RBC1 Consequently, if the timer operates in astable, the period is the same with 'T=tH+tL=0.693(RA+RB)C1+0.693RBC1=0.693(RA+2RB)C1' because the period is the sum of the charge time and discharge time. And since frequency is the reciprocal of the period, the following applies. frequency, 1 1.44 f = --- = ---------------------------------------T R A + 2R B C 1 11 3. Frequency divider By adjusting the length of the timing cycle, the basic circuit of Figure 1 can be made to operate as a frequency divider. Figure 8. illustrates a divide-by-three circuit that makes use of the fact that retriggering cannot occur during the timing cycle. 7 LM555 Figure 8. Waveforms of Frequency Divider Operation 4. Pulse Width Modulation The timer output waveform may be changed by modulating the control voltage applied to the timer's pin 5 and changing the reference of the timer's internal comparators. Figure 9 illustrates the pulse width modulation circuit. When the continuous trigger pulse train is applied in the monostable mode, the timer output width is modulated according to the signal applied to the control terminal. Sine wave as well as other waveforms may be applied as a signal to the control terminal. Figure 10 shows the example of pulse width modulation waveform. +Vcc 4 RA 8 RESET Vcc Trigger 7 DISCH 2 TRIG 6 THRES Output 3 OUT Input GND CONT 5 C 1 Figure 9. Circuit for Pulse Width Modulation Figure 10. Waveforms of Pulse Width Modulation 5. Pulse Position Modulation If the modulating signal is applied to the control terminal while the timer is connected for the astable operation as in Figure 11, the timer becomes a pulse position modulator. In the pulse position modulator, the reference of the timer's internal comparators is modulated which in turn modulates the timer output according to the modulation signal applied to the control terminal. Figure 12 illustrates a sine wave for modulation signal and the resulting output pulse position modulation : however, any wave shape could be used. 8 LM555 +Vcc 4 RA 8 Vcc RESET 7 DISCH 2 TRIG RB 6 THRES Output 3 OUT Modulation GND CONT 5 C 1 Figure 12. Waveforms of pulse position modulation Figure 11. Circuit for Pulse Position Modulation 6. Linear Ramp When the pull-up resistor RA in the monostable circuit shown in Figure 1 is replaced with constant current source, the VC1 increases linearly, generating a linear ramp. Figure 13 shows the linear ramp generating circuit and Figure 14 illustrates the generated linear ramp waveforms. +Vcc RE 4 8 RESET Vcc DISCH 2 R1 7 Q1 TRIG R2 THRES 6 Output 3 OUT GND C1 CONT 5 1 Figure 13. Circuit for Linear Ramp C2 Figure 14. Waveforms of Linear Ramp In Figure 13, current source is created by PNP transistor Q1 and resistor R1, R2, and RE. V CC – V E I C = -------------------------- 12 RE Here, VE is R2 V E = V BE + ---------------------- V CC 13 R1 + R2 For example, if Vcc=15V, RE=20k, R1=5kW, R2=10k, and VBE=0.7V, VE=0.7V+10V=10.7V Ic=(15-10.7)/20k=0.215mA 9 LM555 When the trigger starts in a timer configured as shown in Figure 13, the current flowing through capacitor C1 becomes a constant current generated by PNP transistor and resistors. Hence, the VC is a linear ramp function as shown in Figure 14. The gradient S of the linear ramp function is defined as follows: Vp – p S = ---------------T 14 Here the Vp-p is the peak-to-peak voltage. If the electric charge amount accumulated in the capacitor is divided by the capacitance, the VC comes out as follows: V=Q/C (15) The above equation divided on both sides by T gives us V T---- = Q ----------T C 16 and may be simplified into the following equation. S=I/C (17) In other words, the gradient of the linear ramp function appearing across the capacitor can be obtained by using the constant current flowing through the capacitor. If the constant current flow through the capacitor is 0.215mA and the capacitance is 0.02F, the gradient of the ramp function at both ends of the capacitor is S = 0.215m/0.022 = 9.77V/ms. 10 LM555 Mechanical Dimensions Package Dimensions in millimeters 8-DIP [ .400 10.15 .373 9.46 A ] .036 [0.9 TYP] (.092) [Ø2.337] (.032) [R0.813] PIN #1 .250±.005 [6.35±0.13] PIN #1 B TOP VIEW OPTION 1 TOP VIEW OPTION 2 [ ] .070 1.78 .045 1.14 .310±.010 [7.87±0.25] .130±.005 [3.3±0.13] .210 MAX [5.33] 7° TYP 7° TYP C [ ] .021 0.53 .015 0.37 .001[.025] C .015 MIN [0.38] .140 3.55 .125 3.17 [ ] .100 [2.54] NOTES: A. CONFORMS TO JEDEC REGISTRATION MS-001, VARIATIONS BA B. CONTROLING DIMENSIONS ARE IN INCHES REFERENCE DIMENSIONS ARE IN MILLIMETERS C. DOES NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCHES OR 0.25MM. D. DOES NOT INCLUDE DAMBAR PROTRUSIONS. DAMBAR PROTRUSIONS SHALL NOT EXCEED .010 INCHES OR 0.25MM. E. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994. .300 [7.62] .430 MAX [10.92] .060 MAX [1.52] [ ] +0.127 .010+.005 -.000 0.254-0.000 N08EREVG 11 LM555 Mechanical Dimensions (Continued) Package Dimensions in millimeters 8-SOIC 12 LM555 Ordering Information Product Number Operating Temperature Range LM555CN LM555CM 0 ~ +70C LM555CMX Package Packing Method DIP 8L Rail SOIC 8L Rail SOIC 8L Tape & Reel DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. 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