digital high/low for ADG436.

Hey guys i am working with AD436 Dual SPDT switch IC's (active high). The Digital in's to turn on/off the IC's switches are coming from a data acquisition device capable of producing digital high (3.3V) and low (0 V) states wrt to its ground. The circuit I have built has a separate ground to which the AD436's ground pin is referenced to. The problem is the potential difference between the digital low of the data acquisition device and the circuits ground is higher than the digital input voltage required to turn on the switches in the IC, hence keeping the switches in the IC always on. Tried shorting the grounds of the circuit and the data acquisition device which resulted in two blown IC's. Is there a more elegant solution to this problem?

Funny I just put this on your other post -
Re: Circuit debugging help please.
From past experience with analog switches, similar to what you are using, two things come to mind -

1. Ron (the on resistance) of these switches can changes drastically with supply voltage. Doubling in value from the manufacturers published headline value as the supply voltage is reduced is not unusual.

2. Analog switches are touchy about power supply sequencing. To quote from Analog Device on this topic -
"Care must be taken to ensure correct power-supply sequencing.
Incorrect power-supply sequencing can result in the device being subjected to stresses
beyond those listed in the Absolute Maximum Ratings. Always sequence VDD on first
followed by VSS and the logic signals. An external, analog or digital, signal can then be
safely presented to the source or drain of the switch."
****************Other manufacturers have similar statements.***************

I would advise a good look at the switch manufacturers datasheet if you haven't already done so.
And good luck.

As long as the device voltage specifications can be kept, the ADG ground pin would be connected to the control source. Otherwise, use opto isolation.

As FvM says, the control ground and the ADG ground normally are connected together at some point. If they can't be for some reason, then you need an opto isolator or other means of sending a signal across isolated grounds.

yes, connected the ADG ground to the Digital control units ground earlier today and it works like a charm now. thanks for your input for my various queries. much appreciated.