SMH4042
LOCAL_PCI_RST#:
LOCAL_PCI_RST# is an open-
drain active-low output. It is used to reset the backend
circuitry on the add-in card. It is active whenever the card-
side monitor inputs are below their respective V
TRIP
levels. It may also be driven low by a low input on the
PCI_RST# pin.
LOCAL PCI_RST:
LOCAL PCI_RST is an open-drain
(PFET) active-high output. It operates in parallel with
LOCAL_PCI_RST# providing an active high reset signal
which is required by many 8051 style MCUs. It is active
whenever the card-side monitor inputs are below their
respective V
TRIP
levels. It may also be driven active by a
low input on the PCI_RST# pin.
CARD_3V_MON:
The CARD_3V_MON input monitors
the card-side 3.3V supply. If the input falls below V
TRIP
,
the HEALTHY# and SIGNL_VLD# outputs are de-as-
serted and the reset outputs are driven active.
VGATE3:
VGATE3 is a slew rate limited high side driver
output for the 3.3V external power FET gate. The
VGATE3 output-voltage is generated by an on-board
charge pump.
HST_3V_MON:
The HST_3V_MON input monitors the
host 3.3 volt supply and it is used as a reference for the
circuit breaker comparator. If VCC3 falls below V
TRIP
,
SGNL_VLD# is de-asserted, the high side drivers are
disabled and LOCAL_PCI_RST# is asserted.
CBI_3:
CBI_3 is the circuit breaker input for the low
supply. With a series resistor placed in the supply path
between VCC3 and CBI_3, the circuit breaker will trip
whenever the voltage across the resistor exceeds 50mV.
CARD_5V_MON:
The CARD_5V_MON input monitors
the card-side 5V supply. If the input falls below V
TRIP
, the
HEALTHY# and SIGNL_VLD# outputs are de-asserted
and the reset outputs are driven active.
VGATE5:
VGATE5 is a slew rate limited high side driver
output for the 5V external power FET gate. The output
voltage is generated by an on-board charge pump.
V
CC
:
V
CC
is the power supply pin for the SMH4042 This
input is monitored for power integrity. If it falls below the
5V sense threshold (VTRIP) and the VSEL input is low,
the SGNL_VLD# HEALTHY# signals are de-asserted,
the high side drivers disabled and reset outputs are
asserted. On a
CompactPCI
board, this must be con-
nected to early power.
DEVICE OPERATION
Power-Up Sequence
The SMH4042 is an integrated power controller for any
hot swappable add-in card. The SMH4042 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 sys-
tems.
Insertion Process
As the add-in board is inserted into the backplane physical
connections should be 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). Depending
upon the board configuration early power should be
routed to the VCC pin of the SMH4042. As soon as power
is applied, the SMH4042 will assert the reset outputs to
the backend circuits, turn off the VGATE3/5 outputs
(disabling the external power FETS) and begin outputting
the 1-volt Vref. The 1-volt reference 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 10K ohm).
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 Vref output of the
SMH4042.
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 se-
quence can begin. If, however, the design is based on
high availability requirements the two pins can be actively
driven by the host or combined with a switch input indicat-
ing the ejector handles are fully engaged.
Sequencing
Once the proper card insertion has been assured, the
SMH4042 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 SMH4042 to enable power
sequencing to the card.
Once these conditions are met, the SMH4042 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 using on board circuitry and results
in a slew rate of 250V/s. Different slew rates can be
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SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
