SMH4042
accommodated by either adding an additional capacitor the reset level that will be used to signal valid power. For
between the MOSFET gate and ground or by injecting 3.3V systems, tie VSEL to VCC, for 5V systems, tie VSEL
current into the ISLEW input. All circuitry on the card is to ground.
heldinaresetconditionuntilthe5volts (or3.3volt)supply
is stable and the reset interval timer has timed out the MONITORING POWER SUPPLY HEALTH
150ms reset time. At this point, the reset signals are de-
asserted, and proper operation of the card commences. Monitor Inputs
TheSMH4042hasatotalofsixcomparatorsthatareused
to monitor the health of the host platform supplies and the
card-side (backend) voltages. In hot swap applications
each supply going to the backend logic needs to be
The SMH4042 will monitor the card’s backend voltages.
Once they are at or above the CARD VTRIP levels, the
SMH4042 will drive the HEALTHY# output.
Card Removal Process
monitored at three points.
The card removal process operates in the opposite se-
quence. Fornon-high-availabilitycards, theactionofcard
removal disconnects the BD_SEL# (short pins) from
ground and the SMH4042 will instantly shutdown the
VGATE outputs, change the HEALTHY# status and as-
sert the LOCAL_PCI_RST# output.
The first point is at the source on the host connector, VCC
and HST_3V_MON. If this voltage is not within specifica-
tion, then the down stream sequencing of powering-on
the backend logic will not proceed.
The next stage (the CBI inputs) is one step closer to the
backend logic to monitor the current flowing into the
backend logic. This can not exceed the specification;
however, If it does, then the SMH4042 must turn off the
source to the backend logic.
Because connectors to the host backplane employ the
staggeredpins, powerwillstillbeappliedtotheSMH4042
and the I/O interface circuits. The LOCAL_PCI_RST#
signal will place the interface circuits into a high imped-
ance condition. The pre-charge voltage will be applied to The CARD_5V_MON and CARD_3V_MON inputs are
the I/Os enabling a graceful disengagement from the used to sense the actual voltage level in the backend
active bus. Once the I/O pins are free of the backplane logic. If either comparator detects a low voltage condition
power can then be removed from the SMH4042 and other the backend logic will be placed in a reset condition
early power devices by releasing the long pins.
(LOCAL_PCI_RST# asserted), but the VGATE outputs
will remain active so long as the host voltage and current
sense are valid.
The removal process is slightly different for a high-avail-
ability system. As the ejector handle is rotated the ejector
switch will open, causing a change of state that will VCC vs. HST_3V_MON
activate the ENUM# signal to the host. In response to this The VCC input is the supply input and in a CompactPCI
notification the host will de-assert a hardware controlled application this pin must connect to an early power pin on
BD_SEL# signal. This action will turn on an indicator LED the host connector. The HST_3V_MON input is strictly a
onthecard,notifyingtheoperatoritisnowsafetoproceed voltage monitoring input, it is not a supply input. The
withtheremovalofthecard.Thesequencewillthenfollow operating supply voltage range on the VCC pin is 2.7V to
that outlined for the non-high-availability removal pro- 5.5V, but it will only monitor a 5V supply. This is not an
cess.
Power Configurations
The SMH4042 can be used in 5V-only, 3.3V-only and
mixed voltage systems. For mixed voltage systems, sim-
ply connect the appropriate bus and card power inputs as
indicated. The VSEL pin should be grounded.
For systems with a single power supply, connect VCC and
HST_3V_MON together to the bus power line. Also con-
nect CARD_3V_MON and CARD_5V_MON together to
the card side power. Now the state of VSEL determines
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SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
