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SMH4042S-AGM Datasheet(PDF) 9 Page - Summit Microelectronics, Inc. |
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SMH4042S-AGM Datasheet(HTML) 9 Page - Summit Microelectronics, Inc. |
9 / 28 page 9 2037 8.0 8/8/00 SMH4042 accommodated by either adding an additional capacitor between the MOSFET gate and ground or by injecting current into the ISLEW input. All circuitry on the card is held in a reset condition until the 5 volts (or 3.3 volt) supply is stable and the reset interval timer has timed out the 150ms reset time. At this point, the reset signals are de- asserted, and proper operation of the card commences. 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 The card removal process operates in the opposite se- quence. For non-high-availability cards, the action of card 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. Because connectors to the host backplane employ the staggered pins, power will still be applied to the SMH4042 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 I/Os enabling a graceful disengagement from the active bus. Once the I/O pins are free of the backplane power can then be removed from the SMH4042 and other early power devices by releasing the long pins. 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 activate the ENUM# signal to the host. In response to this notification the host will de-assert a hardware controlled BD_SEL# signal. This action will turn on an indicator LED on the card, notifying the operator it is now safe to proceed with the removal of the card. The sequence will then follow that outlined for the non-high-availability removal pro- 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 the reset level that will be used to signal valid power. For 3.3V systems, tie VSEL to VCC, for 5V systems, tie VSEL to ground. MONITORING POWER SUPPLY HEALTH Monitor Inputs The SMH4042 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, 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. 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. 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 |
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