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SMH4042ASAKN Datasheet(PDF) 9 Page - Summit Microelectronics, Inc. |
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SMH4042ASAKN Datasheet(HTML) 9 Page - Summit Microelectronics, Inc. |
9 / 28 page 2070 9.1 5/27/03 SMH4042A SUMMIT MICROELECTRONICS, Inc. 9 Figure 2. Loss-of-Voltage Timing Sequence Figure 3. Circuit Breaker Timing Sequence 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, 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. 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 issue with a dual supply application. But in a single supply application these two pins must be shorted and VSEL conditioned. 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 4.25V or 4.625V. The HST_3V_MON VTRIP 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 VCC or HST_3V_MON HEALTHY# & LOCAL_PCI_RST# VGATE3 & VGATE5 CARD_3V_MON or CARD_5V_MON DRVREN# & SGNL_VLD# tVTPD tVTR VTRIP 2070 Fig02 VTRIP PCI_RST# VGATE3 & VGATE5 CBI_3 or CBI_5 FAULT# tCBTC 2070 Fig03 |
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