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Protection Circuit for Tristate Push-Pull Drivers

IP.com Disclosure Number: IPCOM000047868D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 74K

Publishing Venue

IBM

Related People

Pollmann, K: AUTHOR [+3]

Abstract

A circuit is described in which the failure of one of the supply voltages causes the push-pull tristate drivers on a semiconductor chip, which are connected to the same output line, to be immediately switched to their high-impedance state. This prevents detrimental short-circuit currents from occurring if the output of one driver is at its up level, while the output of another driver is at its down level. During normal system operation, a priority control prevents such an orthogonal state in that the output of only one driver is switched to its up or down level, while the remaining drivers, connected to the same output line, are switched to their high-impedance state.

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Protection Circuit for Tristate Push-Pull Drivers

A circuit is described in which the failure of one of the supply voltages causes the push-pull tristate drivers on a semiconductor chip, which are connected to the same output line, to be immediately switched to their high-impedance state. This prevents detrimental short-circuit currents from occurring if the output of one driver is at its up level, while the output of another driver is at its down level. During normal system operation, a priority control prevents such an orthogonal state in that the output of only one driver is switched to its up or down level, while the remaining drivers, connected to the same output line, are switched to their high-impedance state. During power-on or power-off or in the case of a power failure, when not all of the supply voltages are present, short-circuit currents may occur, so that neither the priority control nor the drivers function correctly. This is remedied by the circuits of Figs. 1 and 2. Fig. l shows a simplified circuit diagram of a push-pull tristate driver. The additional driver circuit elements, provided for preventing short-circuit currents, are surrounded by a broken line. These elements comprise an input transistor T3, whose emitter is connected to a further input HZ of the control circuit for the high-impedance state. The collector of output transistor T4 of this control circuit is connected to resistors R1, R2 and R3, each of which is connected, through a diode D1, D2 and D3, to one of the driver supply voltages V1, V2 and V3.

Thus, the driver is capable of...