SN74AHC123A SN74AHCT123A SCLA014 SN74AHC/AHCT123A SN74AHCT123 AHC123A AHCT123A - Datasheet Archive

 

SN74AHC123A and SN74AHCT123A SCLA014 October 1999 1 IMPORTANT NOTICE Texas Instruments and its subsidiaries (TI) reserve the

 

Designing With the SN74AHC123A SN74AHC123A and SN74AHCT123A SN74AHCT123A SCLA014 SCLA014 October 1999 1 IMPORTANT NOTICE Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with TI's standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements. CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF DEATH, PERSONAL INJURY, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE ("CRITICAL APPLICATIONS"). TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, AUTHORIZED, OR WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT DEVICES OR SYSTEMS OR OTHER CRITICAL APPLICATIONS. INCLUSION OF TI PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE FULLY AT THE CUSTOMER'S RISK. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right of TI covering or relating to any combination, machine, or process in which such semiconductor products or services might be or are used. TI's publication of information regarding any third party's products or services does not constitute TI's approval, warranty or endorsement thereof. Copyright © 1999, Texas Instruments Incorporated 2 Contents Title Page Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Rules for Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Output Pulse Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Retriggering Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Variation in Output Pulse Duration Due to Temperature and VCC Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 4 6 7 Special Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Setup Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Distribution of Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Delayed-Pulse Generator With Override . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Missing-Pulse Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Low-Power Pulse Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Negative- or Positive-Edge-Triggered One-Shot Multivibrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Pulse-Duration Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Frequency Discriminator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 One-Shot Monostable Multivibrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 List of Illustrations Figure 1 2 3 4 5 6 7 8 9 10 11 12 13 14 A­1 Title Page SN74AHC123A SN74AHC123A and SN74AHCT123A SN74AHCT123A Logic Diagram for Each Multivibrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Timing Component Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Output Pulse Duration vs External Timing Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 External Capacitance vs Multiplier Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Retrigger Pulse Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Input/Output Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Variations in Output Pulse Duration for Various Temperatures and VCC Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Distribution of Units vs Output Pulse Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Delayed-Pulse Generator With Override . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Missing-Pulse Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Low-Power Pulse Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Negative- or Positive-Edge-Triggered One-Shot Multivibrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Pulse-Duration Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Frequency-Discriminator Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 One-Shot Monostable Multivibrator and Function Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 iii iv Abstract This application report is designed to answer any questions that the user may have on the operation of the SN74AHC/AHCT123A SN74AHC/AHCT123A. It also covers the most frequently asked questions and includes detailed instructions on how to calculate the external components required to make the device function correctly. Several circuits using this device also are included to show the versatility of operations that can be performed using this part. Introduction The SN74AHC123A SN74AHC123A and SN74AHCT123A SN74AHCT123A are dual, retriggerable, monostable multivibrators (see Appendix A) that have similar functions. The SN74AHCT123A SN74AHCT123A has TTL inputs and CMOS outputs. The SN74AHC123A SN74AHC123A has CMOS inputs and outputs. These devices require external resistors and capacitors for proper operation, and the resulting RC time constant determines the output pulse duration. These devices are capable of very-long-duration output pulses by retriggering the inputs at appropriate times. An input clear can be used to decrease the output pulse duration. This application report discusses the following points: · · · Rules for operation, which include the output pulse duration, its calculation, and retriggering data Setup of the device in relation to its external components and the variation from unit to unit Applications Features Features of these devices are: · · · · · · · · Retriggerable Edge triggered from active-high or active-low logic inputs Inputs are TTL-voltage compatible for the SN74AHCT123A SN74AHCT123A. VCC range of the SN74AHC123A SN74AHC123A is 2 V to 5.5 V. VCC range of the SN74AHCT123A SN74AHCT123A is 4.5 V to 5.5 V. Clear (CLR) input overrides the other inputs (A and B). When inputs A and B have pulses applied to them, the signal that occurs first determines the pulse that triggers the output. Three inputs (A, B, and CLR) have Schmitt triggers with sufficient hysteresis to handle slow input transition rates with jitter-free triggering at the output. Figure 1 illustrates the logic diagram for both devices. Each multivibrator has two inputs, one that is active low and the other that is active high, allowing leading- and trailing-edge triggering. The output pulse duration can be increased by retriggering the input signal in use. The retrigger pulses at the input must occur after a certain period to be recognized and acted upon by the device. If the input retrigger pulse follows the initial input pulse after 0.30 × the initial output pulse duration, the output is retriggered. CLR terminates the output pulse at any time. Rext/Cext A Cext B Q CLR R Q Figure 1. SN74AHC123A SN74AHC123A and SN74AHCT123A SN74AHCT123A Logic Diagram for Each Multivibrator 1 Table 1. Function Table for the SN74AHC123A SN74AHC123A and SN74AHCT123A SN74AHCT123A INPUTS OUTPUTS CLR A B Q Q L X X X H X L L H H X X L L H H L H # H L H These outputs are based on the assumption that the indicated steady-state conditions at the A and B inputs have been set up long enough to complete any pulse started before the setup. 2 Rules for Operation Proper use depends on observing these rules of operation: · · · · · · · Minimum value of external resistance (RT) is 250 . External capacitance (CT) can have any value. Input voltage range is from 0 V to 5.5 V. SN74AHC123A SN74AHC123A VCC must be 2 V to 5.5 V, and SN74AHCT123A SN74AHCT123A VCC must be 4.5 V to 5.5 V. SN74AHC123A SN74AHC123A and SN74AHCT123 SN74AHCT123 TA can be between ­40°C and 85°C. A switching diode on one side of the capacitor is not needed for the timing scheme. Required connections of RT and CT, for the proper operation of the devices, are shown in Figure 2. CT can be grounded at the Cext terminal. VCC VCC RT RT CT Rext/Cext 1A 1B 1CLR 15 CT 14 Cext 1 Rext/Cext 13 1/2 'AHC123A AHC123A or 1/2 'AHCT123A AHCT123A 2 3 1Q 2A 2B 4 1Q 2CLR 7 6 Cext 9 10 11 5 1/2 'AHC123A AHC123A or 1/2 'AHCT123A AHCT123A 12 2Q 2Q Figure 2. Timing Component Connections Output Pulse Duration The output pulse duration (tw) for both devices is determined primarily by the values of CT and RT. The timing components are connected as shown in Figure 2. The definition of the output pulse duration is shown in equation 1. tw Where: tw = K = RT = CT = +K RT CT (1) pulse duration in ns multiplier factor external timing resistance in k external capacitance in pF If: CT is 1000 pF, K = 1.0 CT is