SYSTEM COMPRISING HOT INSERTABLE/REMOVABLE FUNCTION UNITS

Abstract: In a system comprising a cabinet (2) functional units (6) have to be inserted without switching off the power supply (4). Without precautions damage to the functional unit can arise by the hot insertion. One potential cause of damage is that the voltage on terminal D' which should be -48 Volt becomes higher that the voltage on terminal C' which should be -5 Volt. This can occur due to transient phenomena when hot-inserting the functional unit. To prevent this, a diode (11) is connected between the terminal D' and C'. In an embodiment of the invention, the SLIC (12) is connected to the terminal D' via a diode (10) to prevent that a high current can flow from terminal D', via the diode (11) to terminal C'.

Description: 1 System comprising hot insertable/removable function units. The present invention relates to a system comprising a primary system part with a power supply, a first connector part having at least three supply voltage terminals carrying different voltages generated by the power supply, the system comprises further a removable functional unit having a second connector part inserted in said primary system part such that the first connector part and the second connector part are interconnected. A system according to the preamble is .known from AMD Application Note "Telephone Linecard Powering Considerations with Monolithic SLIC Devices, Publication #19691, August 1997. Such systems find wide spread use in e.g. telephone exchanges, data communication equipment, medical equipment and computers. Said systems comprise a main system part, which can e.g. a cabinet provided with a system power supply, into which functional units, often in the form of plug in cards can be inserted. The advantage of using such insertable functional units is the flexibility obtained, because the number of functional units and their properties can be chosen differently for each system to be built. Often it is desirable that the functional units can be inserted or removed from the primary system part without switching off the system, because a complete shut-down of the system is not tolerable. In order to be able to insert or remove a functional unit without switching off the power supply, measures have to be taken to prevent damage to the primary system part or to the functional unit. It will also limit the maximum current which the system power supply must be able to deliver. This will reduce the system power supply size and costs. In the system according to the above mentioned application note, several measures are taken to prevent damage due to hot insertion/removal of the functional unit. A first measure is using a second connector part having contact fingers of different lengths ensuring a predetermined order of connection of the several parts of the functional unit. Furthermore current limiting resistors are used to limit the inrush currents for two of the at least three supply terminals. These measures result in an increased complexity of the design of the system because bulky resistors have to be added and special connector parts have to be used. 2 The object of the present invention is to provide a system according to the preamble, in which more easy to implement measures are taken to prevent damage due to hot insertion/removal of functional units. To achieve this object, the system according to the present invention is characterized in that the system comprises an unidirectional conduction element connected between at least two of the supply terminals for preventing one of said at least two of the supply terminals to assume a higher voltage than the other of the at least two of the supply terminals. The invention is based on the recognition that damage can arise in particular when the polarity of the voltage difference between two of the supply teiminals is temporarily different from said polarity when the system is in normal use. By connecting an unidirectional conduction element, such as a diode, between said teiminals it is prevented that a large voltage difference having the wrong polarity difference. Experiments have shown that the above measures are sufficient for preventing damage due to hot insertion/removal of a functional unit. Experiments have further shown that the normal inrush currents of the system are also reduced. An embodiment of the invention is characterized in that the unidirectional conduction means comprises a schottky diode. A Schottky diode comprises a junction between a metal and a semiconductor to achieve its operation. Due to this constitution a Schottky diode has a substantial lower threshold voltage than a normal silicon diode. The advantage of using a Schottky diode is that due to the lower threshold voltage almost no current will flow through the circuits connected to the supply terminals when the voltage difference between them temporarily has the wrong polarity. A further embodiment of the invention is characterized in that at least one of the terminals connected to the unidirectional conduction element is coupled to the power supply via a further unidirectional conduction element in order to prevent the flow of a current between said at least two of the supply terminals via the unidirectional conduction element. It may happen that if the voltage difference between said two terminals has the wrong polarity a very large current can flow between said two terminals through the unidirectional conducting element. If a further unidirectional conduction element is introduced 3 in the path from the power supply to a terminal of the unidirectional conducting element, it is prevented that a large current flows between said two terminals. The invention will now be explained with reference to the drawing figure. The sole Figure shows a system according to the invention comprising a primary system part and an insertable/removable functional unit. The system according to the Figure comprises a primary system part comprising a cabinet 2 with a power supply 4. The power supply 4 is arranged for providing three supply voltages i.e. +5 Volt, -5 Volt and -48 Volt to the system. These supply voltages are normally supplied to a backplane in the cabinet in which the first connector parts are mounted. In general the cabinet is arranged for accepting a plurality of functional units, and consequently a plurality of connector parts are present on the backplane to provide power to the plurality of functional units. The three supply voltages (+5 Volt, -5 Volt and -48 Nolt) and Ground are applied to terminals A, C, D and B in the first connector part. The functional unit 6 comprises an integrated SLIC/SLAC chipset 12 having its supply inputs for +5 Nolt, Ground and -5 Nolt directly connected to supply terminals A', B' and C of the second connector part 9. The supply input of the integrated SLIC/SLAC chipset 12 for -48 Nolt is connected to a first terminal of the unidirectional conducting element which is here the anode of a (Schottky) diode 11. Said supply input terminal is also connected to a first terminal of the further unidirectional conduction device, being here the anode of a (Schottky) diode 10. The cathode of the diode 11 is connected to the supply input for -5Nolt of the integrated SLIC/SLAC chipset 12, and the cathode of the diode 10 is connected to a supply terminal D' of the second connector part 9. The integrated SLIC/SLAC chipset 12 has also a plurality of inputs/outputs EXT for connection to telephone terminals. The integrated SLIC (Subscriber Line Interface Circuit)/ SLAC (Subscriber Line Audio Circuit) is arranged for interfacing analog telephone terminals to a digital PCM system. The SLIC part of the chipset 12 is arranged for functions such as powering the subscriber line, ringing etc. It transmits/receives analog audio signals to/from the SLAC part which converts the analog audio signal into digital PCM data or vice versa and it provides the signals to be applied to the backplane of the cabinet of the system. 4 The SLIC/SLAC chipset comprises one or more VLSI-CMOS integrated circuits. These circuits generally have a substrate connection which should be always have the lowest potential present in the system. If the substrate assumes a higher potential than any other part of the integrated circuit, substrate diodes start conducting which can lead to high currents flowing in the supply terminals and the substrate. This may cause damage to the integrated circuit. When a functional unit is hot-inserted it is not guaranteed that this undesired situation cannot temporarily occur. It is normally only guaranteed that the ground connection is the first connection to be made, but for the remaining terminals the order of connection is uncertain. The diode 11 causes that the substrate potential cannot be much higher ( 0.4 Volt) than the voltage on the -5Volt terminal, preventing that substrate diodes start conducting. The diode 10 prevents that the -48 Volt supply can deliver a large current via the diode 11 to the -5Volt supply. This could occur when due to transient phenomena the -48 Volt supply has temporarily a higher potential than the -5 Volt supply. In this way a simple solution to the problems of hot insertion is provided. It is observed that the connections of the diodes have to be reversed if instead of the presently commonly used P-type substrate, integrated circuits having N-type substrate are used.

Claims: CLAIMS: 1. System comprising a primary system part with a power supply, a first connector part having at least three supply voltage terminals carrying different voltages generated by the power supply, the system comprises further a removable functional unit having a second connector part inserted in said primary system part such that the first connector part and the second connector part are interconnected, characterized in that the system comprises an unidirectional conduction element connected between at least two of the supply terminals for preventing one of said at least two of the supply terminals to assume a higher voltage than the other of the at least two of the supply terminals. 2. System according to claim 1, characterized in that the unidirectional conduction means comprises a Schottky diode. 3. System according to one of the previous claims, characterized in that the unidirectional conduction element is present in the removable functional unit. 4. System according to one of the previous claims, characterized in that at least one of the terminals connected to the unidirectional conduction element is coupled to the power supply via a further unidirectional conduction element in order to prevent the flow of a current between said at least two of the supply terminals via the unidirectional conduction element. 5. System part with a power supply and a connector part having at least three supply voltage terminals carrying different voltages generated by the power supply, characterized in that the system part comprises an unidirectional conduction element connected between at least two of the supply voltage terminals for preventing one of said at least two of the supply teiminals to assume a higher voltage than the other of the at least two of the supply terminals. 6 6. System part according to claim 5, characterized in that the unidirectional conduction means comprises a Schottky diode. 7. System part according to claim 5 or 6, characterized in that at least one of the terminals connected to the unidirectional conduction element is coupled to the power supply via a further unidirectional conduction element in order to prevent the flow of a cuιτent between said at least two of the supply teiminals via the unidirectional conduction element. 8. Functional unit for insertion in a primary system part, comprising a first connector part with at least three terminals for connection to a second connector part in the primary system part, characterized in that the functional unit comprises an unidirectional conduction element connected between at least two of the supply terminals for preventing one of said at least two of the supply terminals to assume a higher voltage than the other of the at least two of the supply terminals. 9. Functional unit according to claim 8, characterized in that the unidirectional conduction means comprises a Schottky diode. 10. Functional unit according to claim 7, 8 or 9, characterized in that at least one of the terminals of the unidirectional conduction element is connected to a supply terminal via a further unidirectional conduction element in order to prevent the flow of a current between said at least two of the supply terminals via the unidirectional conduction element.

Inventors: DOORNENBAL JAN J, DOORNENBAL, JAN, J.
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS SVENSKA AB, KONINKLIJKE PHILIPS ELECTRONICS N.V., PHILIPS AB
Application year: 1999
Main classification: H02H3
IPC codes: H02H9, H02J1