Safe Hot Swapping Using the LTC1421 – Design Note 139
James Herr and Robert Reay
transistors, board connection sensing, flexible supply
voltage monitoring, power on reset output, short-circuit
protection and soft or hard reset via software control. 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. Typical Application
Figure 1 shows a typical application using the LTC1421.
The LTC1421 works best with a staggered, 3-level
connector. Ground makes connection п¬Ѓrst 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. The LTCВ®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, …