SMH4042A
MONITORING POWER SUPPLY HEALTH
MONITOR INPUTS
The SMH4042A has a total of six comparators that are
used 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
monitored at three points.
The first point is at the source on the host connector, V
CC
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.
The CARD_5V_MON and CARD_3V_MON inputs are
used to sense the actual voltage level in the backend
logic. If either comparator detects a low voltage condition
the backend logic will be placed in a reset condition
(LOCAL_PCI_RST# asserted), but the VGATE outputs
will remain active so long as the host voltage and current
sense are valid.
V
CC
vs. HST_3V_MON
The V
CC
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 V
CC
pin is 2.7V to
5.5V, but it will only monitor a 5V supply. This is not an
issue with a dual supply application. But in a single supply
application these two pins must be shorted and VSEL
conditioned.
Programmable V
TRIP
Thresholds
The host voltage monitors and the backend voltage
monitors are programmable (by the factory) and provide
a number of options to the end user. The V
CC
monitor V
TRIP
level can be selected for either a 5% or 10% supply with
default values of 4.25V or 4.625V. The HST_3V_MON
V
TRIP
level can be programmed to 2.65V, 2.8V, 2.95V and
3.1V.
The CARD_5V_MON and CARD_3V_MON thresholds
are set in relation to their corresponding host voltage
monitor thresholds. Their offset can be either +50mV or
–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
based on the host power supply falling out of spec.
Also see Figure 2
t
VTPD
DRVREN# &
SGNL_VLD#
t
CBTC
V
CC
or
HST_3V_MON
V
TRIP
VGATE3 &
VGATE5
CBI_3 or
CBI_5
CARD_3V_MON or
CARD_5V_MON
V
TRIP
FAULT#
VGATE3 &
VGATE5
HEALTHY# &
LOCAL_PCI_RST#
t
VTR
PCI_RST#
2070 Fig02
2070 Fig03
Figure 2. Loss-of-Voltage Timing Sequence
SUMMIT MICROELECTRONICS, Inc.
2070
Figure 3. Circuit Breaker Timing Sequence
9.1 5/27/03
9
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
