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INTEGRATED CIRCUITS
AN171 NE558 applications 1988 Dec
Philips Semiconductors
Philips Semiconductors
Application note
NE558 applications
AN171
INTRODUCTION
disabled. After reset is finished, the trigger voltage must be taken high and then low to implement triggering.
The 558 is a monolithic Quad Timer designed to be used in the timing range from a few microseconds to a few hours. Four entirely independent timing functions can be achieved using a tim ing resistor and capacitor for each section. Two sections of the quad may be interconnected for astable operation. All four sections may be used together, in tandem, for sequential timing applications up to several hours. No coupling capacitors are required when connecting the output of one timer section to the input of the next.
The reset voltage must be brought below 0.8V to insure reset.
THE CONTROL VOLTAGE The control voltage is also made available on the 558 timer. This allows the threshold VCC
FEATURES •
100mA output current per section
•
Edge-triggered (no coupling capacitor)
•
Output independent of trigger conditions
R1 C1
RESET S1
R2 5
13
3 1 6 8
TR1
10
11
TR3
15
9 14 16
TR4
2 C2
• •
Wide supply voltage range 4.5V to 16V
7 C3
Timer intervals from microseconds to hours
C4
• Time period equals RC
4
CIRCUIT OPERATIONS
VCC
In the one-shot mode of operation, it is necessary to supply a minimum of two external components (the resistor and capacitor) for timing. The time period is equal to the product of R and C. An output load must be present to complete the circuit due to the output structure of the 558.
R4
12
TR2
RL1
LOAD SWITCH
RL2 RL3
(558) S2
(559)
RL4
R3
SL00990
Figure 1. 558 Test Circuit voltage to be modulated, therefore controlling the output pulse width and duty cycle with an external control voltage. The range of this control voltage is from about 0.5V to VCC minus 1V. This will give a cycle time variation of about 50:1. In a sequential timer with voltage-controlled cycle time, the timing periods remain proportional over the adjustment range.
For astable operation, it is desirable to cross-couple two devices from the 558 Quad. The outputs are direct-coupled to the opposite trigger input. The duty cycle can be set by the ratio of R1C1 to R2C2, from close to zero to almost 100%. An astable circuit using one timer is shown in Figure 5b.
TEST BOARD FOR 558 OUTPUT STRUCTURE 558
The circuit layout can be used to test and characterize the 558 timer. S2 is used to connect the loads to either VCC or ground. The main precaution, in layout of the 558 circuit, is the path of the discharge current from the timing capacitor to ground (Pin 12). The path must be direct to Pin 12 and not on the ground bus. This is to prevent voltage spikes on the ground bus return due to current switching transient. It is also wise to use good power supply bypassing when large currents are being switched.
The 558 structure is open-collector which requires a pull-up resistor to VCC and is capable of sinking 100mA per unit, but not to exceed the power dissipation and junction temperature rating of the die and package. The output is normally low and is switched high when triggered.
RESET A reset function has been made available to reset all sections simultaneously to an output low state. During reset the trigger is
Figure 4. 558 Sequential Timer With Voltage-Controlled Cycle Time (50:1 Range) VCC
VCC
R TRIGGER
TR 0
NOTE: T = RC
RL
R1
RL
R2
T TR
C
T
TR
0
T 0
C1
C2
OUTPUT
OUTPUT
a. Monostable Operation (One-Shot)
b. 558 Astable Operation (Oscillator) VCC
RL
R1
RL
INCREASE FREQUENCY
R2
T
T
TR
TR
C1
CV 0
C2
CV 0
OUTPUT
c. 558 Variable Frequency Oscillator with Fixed Duty Cycle SL00994
Figure 5.
VCC
TRIGGER R1
RL
R1
RL
R1
RL
R1
RL OUTPUT 1
T
T C1
TRIGGER
TR 0
T C1
TR 0
T C1
TR 0
C2
TR 0
OUTPUT 2
OUTPUT 4
OUTPUT 3 TDELA
OUTPUT 1
OUTPUT 2
OUTPUT 3
OUTPUT 4
TOUTPUT
Y
TDELAY 3(R.C.) TOUTPUT )R.C.)
NOT USED
SL00995
Figure 6. 558 Long Time Delay
December 1988
4
Philips Semiconductors
Application note
NE558 applications
AN171
VCC R1 RL 2 5
C1
R1 RL
C1
10
TIME 1
TRIG 01 13
RESET
7
TIME
3
START
R1 RL
6
R1 RL
C1
15
TIME 8
11
TRIG 02 13
9 TRIG 03 13
C1
TIME 14
16
TRIG 04 13 12
10K
a. Ring Counter
VCC
START
RESET
T = RC
01
02
03
04
b. Expected Waveforms
SL00996
Figure 7. A single section of the quad time may be used as a non-precision oscillator. The values given are for oscillation at about 400Hz. T1 ≈ R1C1 and T2 ≈ 2.25 R2C2 for VCC of 15V. The frequency of oscillation is subject to the changes in VCC.
