SMH4042A
DEVICE OPERATION
Power-Up Sequence
The SMH4042A is an integrated power controller for any hot
swappable add-in card. It provides all the signals and
control functions to be compatible with
CompactPCI
Hot
Swap requirements for basic hot swap systems, full hot
swap boards, and high availability systems.
Insertion Process
As the add-in board is inserted into the backplane,
physical connections are made with the chassis in order
to properly discharge any voltage potentials to ground.
The board will first contact the long pins on the backplane
that provide early power (5V, 3.3V and ground). Depend-
ing upon the board configuration, early power should be
routed to the V
CC
pin of the SMH4042A. As soon as power
is applied the SMH4042A will assert the reset outputs to the
backend circuits, turn off the VGATE3 and VGATE5
outputs (disabling the external power FETs) and assert
1VREF. This signal can be used to pre-charge the I/O pins
before they begin to mate with the bus signals. The open
collector HEALTHY# output will be de-asserted. It should
be actively pulled high by an external pull-up resistor
(minimum 10kΩ).
The next pins to mate are the I/Os, and the balance of the
power pins if they are not already mated. The I/Os will
have been pre-charged by the 1VREF output.
The BD_SEL# pins are the last inputs to be driven to their
true state. In most systems these will most likely be
driven to ground when the short pins are mated. This
would indicate the card is fully inserted and the power-up
sequence can begin. If, however, the design is based on
high availability requirements, the two pins can be ac-
tively driven by the host or combined with a switch input
indicating the ejector handles are fully engaged.
Sequencing
Once the proper card insertion has been assured the
SMH4042A will check the status of the Power Enable
signal from the host. This input can be used to power down
individual cards on the bus via software control. It must
by held high in order for the SMH4042A to enable power
sequencing to the card.
When these conditions have been met, the SMH4042A will
drive the VGATE3 and VGATE5 outputs to turn on the
external 3 volt and 5 volt power FETs. The slew rate of
these outputs is controlled to a slew rate of 250V/s.
Different slew rates can be accommodated by either
adding an additional capacitor between the MOSFET gate
and ground or by injecting current into the ISLEW input. All
circuitry on the card is held in a reset condition until the 5V
(or 3.3V) supply is stable and the reset interval timer has
timed out the 150ms reset time. At this point, the reset
signals are de-asserted, and proper operation of the card
commences. See Figure 1, Table 1, and Flow Chart 1.
The SMH4042A will monitor the card’s backend voltages.
Once they are at or above the card V
TRIP
levels the
SMH4042A will drive the HEALTHY# output.
Card Removal Process
The card removal process operates in the opposite
sequence. For non-high-availability cards the action of
card removal disconnects the BD_SEL# (short pins) from
ground and the SMH4042A will instantly shutdown the
VGATE outputs, change the HEALTHY# status, and
assert the LOCAL_PCI_RST# output.
Because connectors to the host backplane employ stag-
gered pins, power will still be applied to the SMH4042A and
the I/O interface circuits. The LOCAL_PCI_RST# signal
will place the interface circuits into a high impedance
condition. The pre-charge voltage will be applied to the
I/Os enabling a graceful disengagement from the active
bus. Once the I/O pins are free of the backplane, power
can be removed from the SMH4042A and other early power
devices by releasing the long pins.
The removal process is slightly different for a high-
availability system. As the ejector handle is rotated the
ejector switch will open, causing a change of state that will
activate the ENUM# signal to the host. In response to this
notification the host will de-assert a hardware controlled
BD_SEL# signal. This action will turn on an indicator LED
on the card, notifying the operator it is now safe to proceed
with the removal of the card. The sequence will then follow
that outlined for the non-high-availability removal pro-
cess.
Power Configurations
The SMH4042A can be used in 5V-only, 3.3V-only and
mixed voltage systems. For systems with a single power
supply, connect V
CC
and HST_3V_MON together to the
bus power line. Also connect CARD_3V_MON and
CARD_5V_MON together to the card side power. Now the
state of VSEL determines the reset level that will be used
to signal valid power. For 3.3V systems tie VSEL to V
CC
,
for 5V systems tie VSEL to ground.
6
2070
9.1 5/27/03
SUMMIT MICROELECTRONICS, Inc.
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
