ADG3247:  Hotswapping

Document created by analog-archivist Employee on Feb 23, 2016
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1.       When you said that:” None of our analog switches can take signals
while the power is removed. There are internal ESD protection diodes between
the signal inputs and the power supply pins which will clamp the signal lines
to ground if power is absent”, did you mean that the device will be damaged
while power is off and signal are on or you just notify me that the outputs
will be grounded?

2.       What did you mean by saying” As far as hot swap capability is
concerned, this needs to be managed at a system level”? Can you let me know the
required circuitry around it?

3.       Which switches are works from two rails: positive and negative?

4.       Which of your switches with two rails are hot-swap?

 

1. Its a diode, so you can imagine the way it functions. If the signal source
is limited in current then the diode will clamp the signal at 0.5V-0.6V. If the
signal source is capable of supplying more than about 10-20mA then the diode
may be damaged. In addition there is the possibility of provoking a latchup
event - see following application note.
http://www.analog.com/library/analogDialogue/archives/35-05/latchup/index.html

2. No I can't recommend specific circuits without without knowing more details
about your system. As an example, the ADM1070 detects a hot swap event on line
cards and turns on-off the required power supplies. Please also see the
attached app note on the ADM1070 use in protecting line cards.
http://www.analog.com/Analog_Root/productPage/productHome/0,,ADM1070,00.html

3. We don't have any bus switches (like ADG3247) with a +/-3V bipolar supply.
The ADG3247 is not suitable due to its +3.3V power supply. We have many
switches which function on dual supplies. see next answer for more details.
I found the following article that you may find interesting on the subject of
using bus switches for hot swap.
http://www.analog.com/library/analogDialogue/archives/36-06/bus_switch/index.htm
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4. The hotswap and hotplug requirement means that the switch is high impedance
when unpowered and remains high impedance until written to. We don't have any
+/-3V devices that have this functionality.

Parts like the ADG509F offer fault protection (high impedance with no supply,
high impedance when input goes outside supply rails). However it needs +/-15V
to operate. We don't make any +/-5V or +/-3V fault protected switches though.

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