Hot-plugging circuit for the interconnection of cards to boards

A hot plug circuit (62) for limiting the surge current generated at the interconnection of first circuit means (30) arranged on a first card (1) and powered by a supply device (2) providing a first supply voltage (ground) on a first supply line (36) and a second supply voltage (+V) on a second supply line (34), with second circuit means (26) on a second card powered by the supply device (2) through a third supply line (74) and fourth supply line (76), where said surge current results from the charge of a decoupling capacitor of capacitance Cd arranged on the second card between the third and fourth supply lines, said hot plug circuit characterized in that it comprises:

• an interconnecting arrangement (14, 12, 22) for coupling the second circuit means to the first circuit means,
• said interconnecting arrangement comprises a first connector (14) having first and second supply pins (40-P, 48-P) connected to the first supply line, with said first pin being longer than said second pin, the first pin being connectable to the third supply line to first supply the first voltage to the second circuit means, and
• the second card comprises a presence indication line (70) connectable to the second supply pin when the interconnection of the first and second cards is completed, which generates on the said presence indication line (70) a first control signal derived from the first supply voltage which is provided to the controlled ramp generation control means to start the generation of the first ramp voltage;
• and
• controlled ramp generation means (82, 84, 102) connected to the first and second supply lines and activated when a connection between the first and third supply lines is completed through the connecting arrangement to start the generation on said fourth supply line of a first ramp voltage Vb derived from the voltages on the first and second supply lines, said ramp voltage having an adjustable slope a=dVb/dt, whereby the surge current i which is equal to a.Cd can be limited to a desired value by adjusting the slope value a.

In a computer system or the like having a system bus including electrical power to which I/O cards or boards are inserted and de-inserted a circuit arrangement for controlling signal transient to allow hot plugging of the card or boards comprising:

• a circuitry for providing desired functions arranged on at least one of the boards;
• a first signal line coupled to the circuitry,
• a second signal line coupled to the circuitry;
• said first signal line and said second signal line providing electrical power to the circuitry;
• a ramp generation control circuit (82) having a first and second states, said circuit being responsive to a first control signal when the card is completely interconnected to the bus or being responsive to a second control signal when the card is not completely interconnected to the bus, whereby the ramp generation control circuit is set to its first and second states which respectively starts the generation of the first ramp voltage or prevents said ramp voltage from being generated;
• and
• a controlled ramp generation means comprising a ramp generating circuit (84, 102) connected to the ramp generation control circuit and responsive to the first and second states of the ramp generation control circuit to generate the first ramp voltage on the second line when the card is completely interconnected to the bus.