SMH4044 Datasheet, PDF (12/20 Pages) Summit Microelectronics, Inc. – Compact PCI Hot-Swap Controller With IPMI Support

SMH4044
Preliminary
MONITORING THE POWER SUPPLY HEALTH
MONITOR INPUTS
The SMH4044 has a total of 8 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, VCC
and HST_3V_MON. If this voltage is not within specifi-
cation 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 cannot exceed the specification;
however, If it does, then the SMH4044 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 and LOCAL_PCI_RST# asserted),
but the VGATE outputs will remain active so long as the
Host voltage and current sense are valid.
Two other monitor inputs, MONITOR1 and MONITOR2,
can be used as additional voltage sensors on either the
Host side or the Card side. When either or both of these
monitor inputs are used on the Host side, their status will
be logically ANDed with the VCC and HST_3V_MON logic.
When either or both are configured to be used as Card side
monitors, their status will be logically ANDed with the
CARD_5V_MON and CARD_3V_MON logic.
This allows the device to be configured in a variety of ways
such as:
A. 4 Host Side, 2 Card Side Monitors
B. 1 Host Side, 3 Card Side Monitors
C. 1 Host Side, 4 Card Side Monitors
The Programmable Monitor Inputs are compared to the
internal 1.25V reference, simplifying the monitoring of
voltages higher than VCC or lower than ground.
In most cases, these monitor inputs will be set to monitor
an under-voltage condition, as are the other voltage
monitors on the chip. Both MONITOR1 and MONITOR2
can be configured to detect over-voltage conditions as
well.
WATCHDOG TIMER
The SMH4044 has an internal Watchdog Timer with a
programmable watchdog interval of 0.8, 1.6 or 3.2 sec-
onds. The watchdog is reset each time a valid I²C address
command is received by the SMH4044. Each time the
SMH4044 generates an acknowledge on the I²C bus, it will
reset the Watchdog Timer. The Watchdog Timer will also
be reset on any CS# edge.
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, 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
issue with a dual supply application, but in a single supply
application these two pins must be shorted and VSEL
properly set.
Programmable VTRIP 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 VCC monitor VTRIP
level can be selected for either a 5% or 10% supply with
default values of 4.375V or 4.625V. The HST_3V_MON
VTRIP level can be programmed to 2.65V, 2.8V, 2.95V or
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 3
Over-current Circuit Breaker
The SMH4044 provides a circuit breaker function to
protect against short circuit conditions or exceeding the
supply limits. By placing a series resistor between the
Host supply and the CBI pins, the breakers will trip
whenever the voltage drop across the series resistor is
greater than the programmed value (25, 50, 75 or 125mV)
for more than 16µs.
Also see Figure 4.
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2057 1.x 8/16/01
SUMMIT MICROELECTRONICS, Inc.