Hot swap connector interface (hot plug, live insertion)

[bruj02]

Most of the application notes and schematics about hot swap
capabilities are geared towards the insertion of a daughter card into
a backplane.

I am wondering if the same principles also apply to lower power
peripherals. Are staggered pins (longer ground pins) such as the ones
found on a USB connector absolutely necessary?

For example, I have always connected peripherals to the parallel port
of my PC without worrying about blowing digital outputs or inputs, and
have never heard about anyone damaging a printer this way.

Is it possible to design a hot swap interface without a specialized
connector? If so, is there a specific logic family that is more robust
for such an application?

 

[Rich Grise]

Most of the application notes and schematics about hot swap
capabilities are geared towards the insertion of a daughter card into
a backplane.

I am wondering if the same principles also apply to lower power
peripherals. Are staggered pins (longer ground pins) such as the ones
found on a USB connector absolutely necessary?

For example, I have always connected peripherals to the parallel port
of my PC without worrying about blowing digital outputs or inputs, and
have never heard about anyone damaging a printer this way.

Is it possible to design a hot swap interface without a specialized
connector? If so, is there a specific logic family that is more robust
for such an application?

I'd recommend against hot-plugging anything into a printer port - in
days of yore, you could swap out a printer adapter for about $5.00;
these days, you blow out the mother board (at least the printer port
part).

Otherwise, then I'd use not only longer ground pins, but longer power
pins, i.e. 3 lengths ground the longest, power mid-size, then signals.

Or, better yet, design your circuit robustly enough to handle
anything/everything that can go wrong.

Good Luck!
Rich

 

[whit3rd]

Most of the application notes and schematics about hot swap
capabilities [seem excessive]
For example, I have always connected peripherals to the parallel port
of my PC without worrying about blowing digital outputs or inputs, and
have never heard about anyone damaging a printer this way.

Is it possible to design a hot swap interface without a specialized
connector? If so, is there a specific logic family that is more robust
for such an application?

Well, it isn't possible without a connector. What constitutes
'specialized' is often a matter of don't-plug-the-wrong-thing-in-here.

Some logic (MC1489A receiver and MC1488 transmitter) is designed for
noisy transient-filled signal wiring, and speed usually suffers
when you use that kind of interface.

Use of a coupling transformer (which can insulate and limit
power transfer by saturating) can allow high speed and
good rejection of static and transients, but requires modulation
and demodulation. That's how Ethernet 10baseT/100baseT/1000baseT
works. Usually you lose DC sensitivity; it was possible to
add DC power to Ethernet, but it wasn't easy.

The reason your printer-connect example works is the third-prong
power pin, which grounds both the printer and computer to your
wall socket before any data connectors are mated. SCSI is similarly
usually capable of hot-plugging.

 

[Robert Baer]

Most of the application notes and schematics about hot swap
capabilities are geared towards the insertion of a daughter card into
a backplane.

I am wondering if the same principles also apply to lower power
peripherals. Are staggered pins (longer ground pins) such as the ones
found on a USB connector absolutely necessary?

For example, I have always connected peripherals to the parallel port
of my PC without worrying about blowing digital outputs or inputs, and
have never heard about anyone damaging a printer this way.

Is it possible to design a hot swap interface without a specialized
connector? If so, is there a specific logic family that is more robust
for such an application?

Of koarse it is posyball and sympal!
Circuitry would sense the connection and then do sequential powering.

 

[Robert Baer]

I'd recommend against hot-plugging anything into a printer port - in
days of yore, you could swap out a printer adapter for about $5.00;
these days, you blow out the mother board (at least the printer port
part).

Otherwise, then I'd use not only longer ground pins, but longer power
pins, i.e. 3 lengths ground the longest, power mid-size, then signals.

Or, better yet, design your circuit robustly enough to handle
anything/everything that can go wrong.

Good Luck!
Rich

....everything?
Earthquakes?
Tornadoes?
Flowing lava?
Floods?
etc?

 

[bruj02]

Most of the application notes and schematics about hot swap
capabilities [seem excessive]
For example, I have always connected peripherals to the parallel port
of my PC without worrying about blowing digital outputs or inputs, and
have never heard about anyone damaging a printer this way.

Is it possible to design a hot swap interface without a specialized
connector? If so, is there a specific logic family that is more robust
for such an application?

Well, it isn't possible without a connector. What constitutes
'specialized' is often a matter of don't-plug-the-wrong-thing-in-here.

Some logic (MC1489A receiver and MC1488 transmitter) is designed for
noisy transient-filled signal wiring, and speed usually suffers
when you use that kind of interface.

Use of a coupling transformer (which can insulate and limit
power transfer by saturating) can allow high speed and
good rejection of static and transients, but requires modulation
and demodulation. That's how Ethernet 10baseT/100baseT/1000baseT
works. Usually you lose DC sensitivity; it was possible to
add DC power to Ethernet, but it wasn't easy.

The reason your printer-connect example works is the third-prong
power pin, which grounds both the printer and computer to your
wall socket before any data connectors are mated. SCSI is similarly
usually capable of hot-plugging.

Thanks for all the feedback. Very insightful.