Safe Hot Swapping Using the LT

When a circuit board is inserted into a live backplane, the
large bypass capacitors on the board can draw huge inrush
currents from the backplane power bus as they charge. The
inrush current, on the order of 10A to 100A, can destroy the
board’s bypass capacitors, metal traces or connector pins.
The inrush current can also cause a glitch on the backplane
power bus, which could force all of the other boards in the
system to reset. In addition, the system data bus can be
disrupted when the board’s data pins make or break
contact.
The LTC®1421 can turn on two positive and one negative
board supply voltages at a programmable rate, allowing a
board to be safely inserted in, or removed from, a live
backplane. The device provides internal charge pumps for
Figure 1. LTC1421 Typical Application
driving the gates of external N-channel pass transistors,
board connection sensing, flexible supply voltage monitoring,
power on reset output, short-circuit protection and
soft or hard reset via software control.
Typical Application
Figure 1 shows a typical application using the LTC1421.
The LTC1421 works best with a staggered, 3-level connector.
Ground makes connection first to discharge any static
build-up. VCC, VDD and VEE make connection second and
the data bus and all other pins last. The connection sense
pins CON1 and CON2 are located on opposite ends of the
connector to allow the board to be rocked back and forth
during insertion.