LM555/NE555/SA555 Single Timer

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1 Single Timer Features High Current Drive Capability (00mA) Adjustable Duty Cycle Temperature Stability of 0.005%/ C Timing From µsec to Hours Turn off Time Less Than µsec Applications Precision Timing Pulse Generation Time Delay Generation Sequential Timing Description The LM555/NE555/SA555 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. -DIP -SOP Internal Block Diagram R R R Trigger Comp. Discharging Tr. Discharge Output OutPut Stage F/F Comp. Threshold Reset Vref 5 Control Voltage Rev Fairchild Semiconductor Corporation

2 Absolute Maximum Ratings (TA = 5 C) Parameter Symbol Value Supply Voltage VCC V Lead Temperature (Soldering 0sec) TLEAD 00 C Power Dissipation PD 00 mw Operating Temperature Range LM555/NE555 SA555 TOPR 0 ~ +0-0 ~ +5 Storage Temperature Range TSTG -5 ~ +50 C Unit C

3 Electrical Characteristics (TA = 5 C, VCC = 5 ~ 5V, unless otherwise specified) Parameter Symbol Conditions Min. Typ. Max. Unit Supply Voltage VCC V Supply Current (Low Stable) (Note) ICC VCC = 5V, RL = - ma VCC = 5V, RL = ma Timing Error (Monostable) Initial Accuracy (Note) Drift with Temperature (Note) Drift with Supply Voltage (Note) ACCUR t/ T t/ VCC RA = kω to00kω C = 0.µF % ppm/ C %/V Timing Error (Astable) Intial Accuracy (Note) Drift with Temperature (Note) Drift with Supply Voltage (Note) Control Voltage Threshold Voltage ACCUR t/ T t/ VCC VC VTH RA = kω to 00kΩ C = 0.µF Notes:. When the output is high, the supply current is typically ma less than at VCC = 5V.. Tested at VCC = 5.0V and VCC = 5V.. This will determine the maximum value of RA + RB for 5V operation, the max. total R = 0MΩ, and for 5V operation, the max. total R =.MΩ.. These parameters, although guaranteed, are not 00% tested in production % ppm/ C %/V VCC = 5V V VCC = 5V...0 V VCC = 5V V VCC = 5V -. - V Threshold Current (Note) ITH µa Trigger Voltage VTR VCC = 5V... V VCC = 5V V Trigger Current ITR VTR = 0V µa Reset Voltage VRST V Reset Current IRST ma Low Output Voltage High Output Voltage VOL VOH VCC = 5V ISINK = 0mA ISINK = 50mA VCC = 5V ISINK = 5mA VCC = 5V ISOURCE = 00mA ISOURCE = 00mA.5 VCC = 5V ISOURCE = 00mA V V V.5. - V V.5. - V Rise Time of Output (Note) tr ns Fall Time of Output (Note) tf ns Discharge Leakage Current ILKG na

4 Application Information Table below is the basic operating table of 555 timer: Threshold Voltage Trigger Voltage Discharging Tr. Reset(PIN ) Output(PIN ) (Vth th)(pin ) (Vtr tr)(pin ) (PIN ) Don't care Don't care Low Low ON Vth > / Vth > / High Low ON / < Vth < / / < Vth < / High - - Vth < / Vth < / 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 / of the supply voltage while the timer output is high, the timer's internal discharge Tr. turns on, lowering the threshold voltage to below / 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 / of the supply voltage, the timer's internal discharge Tr. turns off, increasing the threshold voltage and driving the timer output again at high.. Monostable Operation Table. Basic Operating Table + Trigger RL RESET TRIG OUT DISCH THRES CONT 5 C RA C Capacitance(uF) R =kω=k =k A 0kΩ0k 0k 00kΩ00k 00k MΩM M MΩ0M 0M 0 Time Delay(s) Figure. Monoatable Circuit Figure. Resistance and Capacitance vs. Time delay(td) Figure. Waveforms of Monostable Operation

5 Figure illustrates a monostable circuit. In this mode, the timer generates a fixed pulse whenever the trigger voltage falls below /. When the trigger pulse voltage applied to the # pin falls below / 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 C and setting the flip-flop output at the same time. The voltage across the external capacitor C, VC increases exponentially with the time constant t=ra*c and reaches / at td=.ra*c. Hence, capacitor C is charged through resistor RA. The greater the time constant RAC, the longer it takes for the VC to reach /. In other words, the time constant RAC controls the output pulse width. When the applied voltage to the capacitor C reaches /, the comparator on the trigger terminal resets the flip-flop, turning the discharging Tr. on. At this time, C begins to discharge and the timer output converts to low. In this way, the timer operating in the monostable repeats the above process. Figure shows the time constant relationship based on RA and C. Figure 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 / 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 /. Figure shows such a timer output abnormality. Figure. Waveforms of Monostable Operation (abnormal). Astable Operation + 00 RESET TRIG DISCH THRES RA RB Capacitance(uF) 0 0. M MΩ M M 0M 0MΩ 0M 0M 0k 0kΩ 0k 0k 00k 00kΩ 00k 00k k kω k k (R +R ) A B RL OUT CONT 5 C C 0.0 E- 00m 0 00 k Frequency(Hz) 0k 00k Figure 5. Astable Circuit Figure. Capacitance and Resistance vs. Frequency 5

6 Figure. Waveforms of Astable Operation An astable timer operation is achieved by adding resistor RB to Figure 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 VC increases by exponential function with the time constant (RA+RB)*C. When the VC, or the threshold voltage, reaches /, 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 C discharges through the discharging channel formed by RB and the discharging Tr. When the VC falls below /, the comparator output on the trigger terminal becomes high and the timer output becomes high again. The discharging Tr. turns off and the VC rises again. In the above process, the section where the timer output is high is the time it takes for the VC to rise from / to /, and the section where the timer output is low is the time it takes for the VC to drop from / to /. When timer output is high, the equivalent circuit for charging capacitor C is as follows: R A R B C Vc(0-)=/ dv c C dt V cc V( 0-) = ( ) R A + R B V ( 0+ ) = V ( ) C CC t V C ( t) V CC ( R --e A + R B )C = ( ) Since the duration of the timer output high state(th) is the amount of time it takes for the VC(t) to reach /,

7 V ( t) C t H - --V = V CC CC --e ( R A + R B )C = ( ) t = C ( R + R )In = 0.9( R + R )C ( 5) H A B A B The equivalent circuit for discharging capacitor C, when timer output is low is, as follows: R B C V C (0-)=/ R D dv C C dt V C ( t) V R + R C = 0 ( ) A B t ( R A + R D )C = --V CC e ( ) Since the duration of the timer output low state(tl) is the amount of time it takes for the VC(t) to reach /, t L ( R A + R D )C --V CC = --V CC e ( ) t = C ( R + R )In = 0.9( R + R )C ( 9) L B D B D Since RD is normally RB>>RD although related to the size of discharging Tr., tl=0.9rbc (0) Consequently, if the timer operates in astable, the period is the same with 'T=tH+tL=0.9(RA+RB)C+0.9RBC=0.9(RA+RB)C' 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, f. = -- = ( ) T ( R + R )C A B. Frequency divider By adjusting the length of the timing cycle, the basic circuit of Figure can be made to operate as a frequency divider. Figure. illustrates a divide-by-three circuit that makes use of the fact that retriggering cannot occur during the timing cycle.

8 Figure. Waveforms of Frequency Divider Operation. 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 0 shows the example of pulse width modulation waveform. + R A Trigger RESET TRIG DISCH Output OUT THRES Input CONT 5 C Figure 9. Circuit for Pulse Width Modulation Figure 0. 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, 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 illustrates a sine wave for modulation signal and the resulting output pulse position modulation : however, any wave shape could be used.

9 + RESET TRIG DISCH R A R B Output OUT THRES Modulation CONT 5 C Figure. Circuit for Pulse Position Modulation Figure. Waveforms of pulse position modulation. Linear Ramp When the pull-up resistor RA in the monostable circuit shown in Figure is replaced with constant current source, the VC increases linearly, generating a linear ramp. Figure shows the linear ramp generating circuit and Figure illustrates the generated linear ramp waveforms. + RESET TRIG DISCH RE Q R Output OUT THRES CONT 5 C C R Figure. Circuit for Linear Ramp Figure. Waveforms of Linear Ramp In Figure, current source is created by PNP transistor Q and resistor R, R, and RE. V V I = CC E ( ) C R E Here, V E is R V = V V ( ) E BE R + R CC For example, if =5V, RE=0kΩ, R=5kW, R=0kΩ, and VBE=0.V, VE=0.V+0V=0.V Ic=(5-0.)/0k=0.5mA 9

10 When the trigger starts in a timer configured as shown in Figure, the current flowing through capacitor C becomes a constant current generated by PNP transistor and resistors. Hence, the VC is a linear ramp function as shown in Figure. The gradient S of the linear ramp function is defined as follows: V p p S = ( ) T 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 (5) The above equation divided on both sides by T gives us V --- T Q T = ( ) C and may be simplified into the following equation. S=I/C () 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 0.5mA and the capacitance is 0.0µF, the gradient of the ramp function at both ends of the capacitor is S = 0.5m/0.0µ = 9.V/ms. 0

L M 5 5 5/N E 5 5 5/S A 5 5 5

L M 5 5 5/N E 5 5 5/S A 5 5 5 S i n g l e T i m e r www.fairchildsemi.com Features High Current Drive Capability (00mA) Adjustable Duty Cycle Temperature Stability of 0.005%/ C Timing From µsec to Hours