Live Insertion
SDYA012
October 1996
1
IMPORTANT NOTICE
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Copyright
©
1996, Texas Instruments Incorporated
2
Contents
Title
Page
Abstract
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
1 Introduction
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
2 Internal Construction of Integrated Circuits
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3 Operating Conditions When Changing Modules With the Supply Voltage On
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1 GND and the signal line (SL) make contact first; the output of circuit N1 is low
. . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 V
CC
and the signal line (SL) make contact first; the output of circuit N1 is low
. . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 GND and the signal line (SL) make contact first; the output of circuit N1 is high
. . . . . . . . . . . . . . . . . . . . . . . . .
3.4 V
CC
and the signal line (SL) make contact first; the output of circuit N1 is high
. . . . . . . . . . . . . . . . . . . . . . . . . .
3.5 V
CC
and GND make contact first . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
4
4
4
5
5
4 Simple Circuit Modifications
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
5 Avoidance of Bus Conflicts
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
6 Avoidance of Disturbances on the System Bus
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
7 Special Bus-Interface Circuits
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
8 Avoidance of Disturbances to the Supply Voltage
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
9 Summary
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
Acknowledgment
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
List of Illustrations
Figure
1
2
3
4
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6
7
8
9
10
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14
Title
Page
Diodes in the Inputs and Outputs of Integrated Circuits
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
Voltage-Monitoring Circuit in BiCMOS ICs
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
Simplified Circuit to Show Current Paths When Connecting a Module to a System
. . . . . . . . . . . . . . . . . . . . . . . . .
4
Improved Circuit Using Bipolar or BiCMOS Circuits
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
Curve for Calculating the Short-Circuit Currents That Occur With Bus Conflicts
. . . . . . . . . . . . . . . . . . . . . . . . . . .
6
Monitoring Bus-Interface Circuits
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
Connecting a Capacitor to a Line
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
Voltage Peaks When Making Contacts to Signal Lines (Without Voltage Bias)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
Connection of a Capacitor to a Line (With Voltage Bias)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
Voltage Peaks When Making Contacts to Signal Lines (With Voltage Bias)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
Generation of the Voltage Bias and Control of the Interface
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
Generation of the Voltage Bias and Control in the SN74ABTE16245
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
Bus-Interface Control in ETL Circuits
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
Bus-Interface Control With BTL Circuits
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
Widebus is a trademark of Texas Instruments Incorporated.
iii
List of Illustrations (Continued)
15
16
17
18
Equivalent Circuit of the Current Supply to a Module
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
Transient Behavior of the Supply Voltage at Switch On, With Various Degrees of Damping
. . . . . . . . . . . . . . . . .
15
Switch-On Delay Circuit Using a MOS Transistor
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
Decentralized Power Supply With Limiting of Switch-On Current
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
iv
Abstract
In many current applications, there is a requirement to exchange modules in electronic systems while the supply voltage
remains on. This procedure is commonly known as live insertion. To understand this requirement, consider the case of an
electronic telephone exchange in which replacing modules for maintenance or repair must be possible at any time without
interrupting the operation of the system. To avoid damage to components, and any interruption of operation when changing
modules in this way, additional circuitry modifications are necessary.
This report describes the phenomena that occur during live insertion, then presents circuit proposals to solve the potential
problems that might otherwise arise.
1 Introduction
For many years, diverse functions and processes have been monitored and controlled successfully by electronic systems. The
advantages of electronic controls in such cases (compared with manual or mechanical controls) are lower operating costs and
the improved reliability that electronics now provide. However, faults also can arise in such electronic systems, which then
require repair. By using modular construction for the equipment, it is possible to quickly exchange a defective module and clear
the fault.
With most equipment, it is necessary to switch off the supply voltage during the exchange of the modules to avoid incorrect
operation or destruction of components. In many cases–an obvious example is the computer in an office–the exchange of
modules while the equipment is turned off is permissible.
In many electronic systems, switching off the equipment to exchange a defective module is unacceptable. Examples include
an electronic telephone exchange, the switching control center of an electric utility, or the computer that processes data in the
air-traffic control center of an airport. In all of these cases, when a fault is found in a module, exchanging this module in a
running system without disturbing or otherwise compromising the rest of the system functions must be possible.
The engineer planning and developing electronic systems for such applications must consider the operating states that can arise
and meet these requirements by choosing appropriate components and circuitry layout.
A distinction must be made at this point between two different cases. In the first, it is necessary only to ensure that a module
or a part of the installation can be exchanged during operation without switching off the system and without damaging it. In
such cases, it can be acceptable (for reasons described later) that the operation of the equipment is disturbed. An example is
the installation or exchange of a printer for an operating office computer. The primary requirement is the simple and safe
operation of the entire system; in this case, the requirements can be fulfilled by choosing appropriate components for
the interfaces.
In the second case, the additional requirement must be met that, during exchange of the modules, the components involved
should neither be damaged, nor should the operation be disturbed. To ensure this, beside choosing the appropriate components,
the development engineer also must incorporate additional circuit modifications to allow continuous and reliable operation
of the system.
This applications report provides the development engineer with suggestions for fulfilling these requirements. The report
begins with the choice of the most appropriate components for the application, and continues with a description of circuit
modifications that are necessary under the operating conditions described.
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