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參數(shù)資料
| 型號： | S39421S |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Hot Swap Voltage Controller |
| 中文描述： | 電壓熱插拔控制器 |
| 文件頁數(shù)： | 21/28頁 |
| 文件大?。?/td> | 201K |
| 代理商： | S39421S |
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S39421
21
2024 9.0 8/8/00
Using the S39421 as the Primary Control Circuit
on a VME Live Insertion Card
High availability is a key feature of many types of systems
today. Whether the system is a central office switch, a
private branch exchange or a server it is important the
system stay up and running while adding new services
(add-in cards) or replacing faulty boards. Therefore, a
means for inserting and removing cards while the entire
system is powered-on (live) is a necessity.
Live insertion poses a number of challenges for the add-
in card designer. For live insertion to be trouble free we
first need to prevent damage to components on the add-
in card due to improper supply sequencing. Secondly,
voltage drop on the system power busses must be pre-
vented in order to avoid unwanted system reset condition.
Lastly, the integrity of the system
’
s signals needs to be
maintained when additional circuitry is connected to the
bus.
Based upon the proposed Live Insertion System Require-
ments the S39421 is an ideal candidate as the add-in
card
’
s live insertion controller.
Sequencing the Voltages
The proposed live insertion specification (see references)
outlines 26 operational steps during the insertion of a
card. These are broken down into two major categories;
the
“
Insertion Process
”
and the
“
Typical Board Recogni-
tion Process.
”
The first 6 steps have to do with the insertion of the card
and sequencing the discharge of any voltage potentials
so that by the time the board is ready to make contact with
the backplane no ESD discharges will occur. Even though
the balance of the actions tend to overlap they can be
viewed as two operations: the add-in card/backend logic
sequencing and the backplane/add-in card interface se-
quencing.
Add-in Card/Backend Logic Sequencing
The process of electrical insertion begins with the contact
of special ground and voltage pins. These are longer than
the signal and power pins and they are physically located
at opposite ends of the connector. The voltage pins are
labeled Vpc (pre-charge Voltage), this is the backplane
’
s
5 volt supply and the intent is for this voltage to be used
to power the sequencing circuitry, any ASICs that inter-
face to the bus and to pre-charge the
‘
bus-side
’
lines of the
signal transceivers.
The PC board should be laid out so that ground is routed
to all circuits, i.e. grounds should not be linked via the PCB
connector. Vpc should be tied directly to the VCC5 pin on
the S39421 and the device will immediately begin driving
its backend circuit control signals [SGNL_VLD,
CARD_V_VLD, RESET and RESET] and it will place the
voltage ramp control signals [VGATE3, VGATE5 and
DRVREN] in the off state.
The next step is for the controller to recognize that the
board is properly seated in the connector. VME has an
optional feature that lends itself ideally to this step of the
operation; the ejector handles can be used to activate a
switch when they are fully rotated and locked. Switch
closure can be used as the PND1 and PND2 inputs on the
S39421. The pull-up resistor used for this implementation
must be tied to Vpc because the backend voltages will not
yet have been switched on by the S39421.
FIGURE 24: ILLUSTRATION OF CARD INJECTOR/EJECTOR SWITCH CIRCUIT
PND1
Vpc
S
Ejector and Switch Open
PND1 Pulled High
Vpc
PND1
S
Card Seated Ejector Locked
and PND1 Driven to Gnd
2024 ILL27.0
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