SENSE

TIMER

UV

GATE

OV

PWRGD

LM5068

Q1

(GND)

(-48V)

+

+

+ C

F

LM5068

PLUG-IN BOARD

CL

LIVE

BACKPLANE

+

LM5068

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SNVS254C – JANUARY 2004 – REVISED MARCH 2013

FUNCTION DESCRIPTION

The LM5068 is designed to facilitate the insertion and removal of circuit cards into live backplanes in a controlled

manner. Because the supply bypass capacitors on the circuit card can draw large transient currents, it is critical

to control the supply current during insertion to limit system power glitches and connector damage. Controlling in-

rush current prevents other boards in the system from resetting during board insertion. Load short-circuit

protection is accomplished by active current limiting of the load current. The topology of the LM5068 is illustrated

in the simplified application circuit shown in Figure 23.

Figure 23. LM5068 Topology

Start-Up Operation

The LM5068 resides on a removable circuit card. Power is applied to the load or power conversion circuitry

through an external N-Channel MOSFET switch and current sense resistor.

When power is initially applied to the card, the gate of the external MOSFET is held low. When certain interlock

conditions are met, a turn-on sequence begins and an internal 60 µA current source charges the gate of the

MOSFET. To initiate the start-up sequence, all of the following interlock conditions must be satisfied:

•

•

•

•

•

When all of the interlock conditions are met, a 6 µA TIMER current source is enabled to charge the timer

into the MOSFET gate.

Figure 24. Hot Swap Controller

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