S39421 datasheet(21/28 Pages) SUMMIT

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S39421

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

Ejector and Switch Open

PND1 Pulled High

Vpc

PND1

Card Seated Ejector Locked

and PND1 Driven to Gnd

2024 ILL27.0

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