SMH4042A
MONITORING POWER SUPPLY HEALTH
MONITORINPUTS
VCC vs. HST_3V_MON
The VCC input is the supply input and in a CompactPCI
application this pin must connect to an early power pin on
the host connector. The HST_3V_MON input is strictly
a voltage monitoring input, it is not a supply input. The
operating supply voltage range on the VCC pin is 2.7V to
5.5V, but it will only monitor a 5V supply. This is not an
issuewithadualsupplyapplication. Butinasinglesupply
application these two pins must be shorted and VSEL
conditioned.
The SMH4042A has a total of six comparators that are
usedtomonitorthehealthofthehostplatformsuppliesand
thecard-side(backend)voltages. Inhotswapapplications
each supply going to the backend logic needs to be
monitored at three points.
The first point is at the source on the host connector, VCC
and HST_3V_MON. If this voltage is not within specifi-
cation, 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 SMH4042A must turn off the
source to the backend logic.
Programmable VTRIP Thresholds
The host voltage monitors and the backend voltage
monitors are programmable (by the factory) and provide
anumberofoptionstotheenduser. TheVCCmonitorVTRIP
level can be selected for either a 5% or 10% supply with
The CARD_5V_MON and CARD_3V_MON inputs are default values of 4.25V or 4.625V. The HST_3V_MON
used to sense the actual voltage level in the backend VTRIP levelcanbeprogrammedto2.65V, 2.8V, 2.95Vand
logic. If either comparator detects a low voltage condition 3.1V.
the backend logic will be placed in a reset condition
The CARD_5V_MON and CARD_3V_MON thresholds
(LOCAL_PCI_RST# asserted), but the VGATE outputs
are set in relation to their corresponding host voltage
will remain active so long as the host voltage and current
monitor thresholds. Their offset can be either +50mV or
sense are valid.
–50mV. This allows the designer to select +50mV if they
want a collapse in the backend voltage to trigger a local
reset condition prior to the host supply collapsing and
powering down the board without warning. Alternatively
they can choose –50mV to trigger a board shutdown
V
TRIP
based on the host power supply falling out of spec.
V
or
CC
HST_3V_MON
Also see Figure 2
t
VTPD
DRVREN# &
SGNL_VLD#
t
CBTC
CBI_3 or
CBI_5
VGATE3 &
VGATE5
FAULT#
V
TRIP
CARD_3V_MON or
CARD_5V_MON
VGATE3 &
VGATE5
t
VTR
HEALTHY# &
LOCAL_PCI_RST#
PCI_RST#
2070 Fig02
2070 Fig03
Figure 2. Loss-of-Voltage Timing Sequence
Figure 3. Circuit Breaker Timing Sequence
SUMMIT MICROELECTRONICS, Inc.
2070 9.1 5/27/03
9
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
