SMH4042A Datasheet, PDF (20/28 Pages) Summit Microelectronics, Inc. – Distributed Power Hot-Swap Controller for CompactPCI

SMH4042A
I/O Pre-charge
The CompactPCI specs require the add-in board to pre-
charge the board’s I/Os before making contact with bus
pins, and sets the pre-charge voltage at 1V ±0.1V. The
SMH4042A provides an accurate 1V reference output that
is accurate and stable prior to the medium length pins
making contact. The 1VREF output should be the
reference input to a unity gain op amp circuit. Figure 17
is a typical implementation utilizing a common op amp.
V_CC5
Early Power
SMH4042A
1V_REF
–
+
LMV321
Resistor Array
Figure 17. I/O Pre-charge Circuit
2070 Fig17
SPECIAL CONSIDERATIONS
The example application shown in Figure 11 shows both
of the BD_SEL inputs being used independently. These
two inputs are effectively ANDed internally and they must
both be low before any sequencing will proceed. In most
design cases the BD_SEL1# connection to an injector
switch is redundant and realistically can be grounded.
The CompactPCI Hot Swap specification does provide a
mechanism for implementing high availability systems
using “Full Hot Swap” boards. This capability entails
integrating the injector/ejector handle, the blue LED and
a board status signal. Section 2.3.2 of the CompactPCI
Hot Swap specification states the following.
• “A signal (ENUM#) is provided to notify the system
host that either a board has been freshly inserted or is
about to be extracted.”
• “A switch, actuated with the lower ejector handle of
the board, is used to signal the insertion or impending
extraction of a board.”
• “A blue LED, located on the board is illuminated when
it is permissible to extract a board.”
Figure 18 illustrates a possible implementation of the
circuits needed. It should be noted this will require a
status register that works in conjunction with the switch
logic to generate the ENUM# signal. Notice the blue LED
circuit and the active high reset output used to activate a
current boost circuit for the LED. The sequence of
operations is as follows:
• The long pins engage.
•
Power is supplied to the SMH4042A, the LED and
the BD_SEL pull-up resistor.
•
V(I/O) is either the early 5V or the early 3V,
dependent upon the interface operating levels.
•
The LED is illuminated by LOCAL_PCI_RST#
going low.
20
2070 9.1 5/27/03
SUMMIT MICROELECTRONICS, Inc.