SLFS043I September   1983  – July 2019 TLC555

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions: D, P, PS, and JG Packages
    2.     Pin Functions: PW and FK
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 Recommended Operating Conditions
    3. 6.3 Thermal Information
    4. 6.4 Electrical Characteristics: VDD = 2 V for TLC555C, VDD = 3 V for TLC555I
    5. 6.5 Electrical Characteristics: VDD = 5 V
    6. 6.6 Electrical Characteristics: VDD = 15 V
    7. 6.7 Operating Characteristics
    8. 6.8 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Monostable Operation
      2. 7.3.2 Astable Operation
      3. 7.3.3 Frequency Divider
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Missing-Pulse Detector
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curve
      2. 8.2.2 Pulse-Width Modulation
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Application Curve
      3. 8.2.3 Pulse-Position Modulation
        1. 8.2.3.1 Design Requirements
        2. 8.2.3.2 Detailed Design Procedure
        3. 8.2.3.3 Application Curves
      4. 8.2.4 Sequential Timer
        1. 8.2.4.1 Design Requirements
        2. 8.2.4.2 Detailed Design Procedure
        3. 8.2.4.3 Application Curve
      5. 8.2.5 Designing for Improved ESD Performance
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.3.2 Astable Operation

As shown in Figure 12, adding a second resistor, RB, to the circuit of Figure 9 and connecting the trigger input to the threshold input causes the timer to self-trigger and run as a multi-vibrator. The capacitor C charges through RA and RB and then discharges through RB only. Therefore, the duty cycle is controlled by the values of RA and RB.

This astable connection results in capacitor C charging and discharging between the threshold-voltage level
(≈ 0.67 × VCC) and the trigger-voltage level (≈ 0.33 × VCC). As in the monostable circuit, charge and discharge times (and, therefore, the frequency and duty cycle) are independent of the supply voltage.

TLC555 app_fig4_lfs022.gif
A. Decoupling CONT voltage to ground with a capacitor can improve operation. This should be evaluated for individual applications.
Figure 12. Circuit for Astable Operation
TLC555 app_fig5_lfs022.gif
RA = 5 kΩ RB = 3 kΩ C = 0.15 µF
See Figure 12
Figure 13. Typical Astable Waveforms

Figure 13 shows typical waveforms generated during astable operation. The output high-level duration tH and low-level duration tL for frequencies below 100 kHz can be calculated as follows:

Equation 1. TLC555 eq1_slfs022.gif
Equation 2. TLC555 eq2_slfs022.gif

Other useful relationships are shown below:

Equation 3. TLC555 eq3_slfs022.gif
Equation 4. TLC555 eq4_slfs022.gif
Equation 5. TLC555 eq5_slfs022.gif
Equation 6. TLC555 eq6_slfs022.gif
Equation 7. TLC555 eq7_slfs022.gif

The formulas (1-7) do not account for any propagation delay times from the TRIG and THRES inputs to DISCH output. These delay times add directly to the period and overcharge the capacitor which creates differences between calculated and actual values that increase with frequency. In addition, the internal on-state resistance ron during discharge adds to RB to provide another source of timing error in the calculation when RB is very low. The equations below provide better agreement with measured values. The formulas Equation 8 represent the actual low and high times when used at higher frequencies because propagation delay and discharge on resistance is added to the formulas. Because the formulas are complex, a calculation tool, TLC555 Design Calculator can be used to calculate the component values.

Equation 8. TLC555 equation_02_slfs043.gif
TLC555 ai_astable_op.gifFigure 14. Trigger and Threshold Voltage Waveform
TLC555 D012_AstabF4_SLFS043.gifFigure 15. Free-Running Frequency vs Timing Capacitance
Resistance = RA + 2 × RB