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Current derating for multiplexers

Question asked by lbidaux on Jan 26, 2016
Latest reply on Oct 6, 2016 by lbidaux

Hello all,

 

 

I am currently designing a multiplexed data acquisition system with relatively high current requirements. My objective right now is to multiplex 8:1 channels with 250 mA current max. Max ambient is 50°C. Available supplies are +/-15V and +/-8V (I need dual supplies for my application, as inputs range from -6V to +5V. I cannot find beyond-the-rail MUXes with these signal input requirements.)

 

The ADG1608 in LFCSP packaging seems to be the only available choice on the market. This reference is featured as designed for +/-8V operation (typical curves include this supply range), which is good for my application.

+/-5V operation shows 470 mA at 25°C and 255 mA at 85°C (and 120 mA @ 125°C)

 

I suppose that +/-8V operation lowers Ron, which in turn allows higher current.

I also suppose that current derating is more or less linear with respect to temperature.

 

Are those suppositions correct? With these suppositions, I can correctly use the ADG1608 at 250 mA continuous curent with +/-8V supplies and 50°C ambient.

In general,is there a rule on how I can derate multiplexer current-carrying capabilities with respect to supply range and temperature range, and if applicable with any other parameter?

 

 

Additional questions:

-Does self-heating impact operation in a significant way? (ie. for example will Ron still be 7 Ohm max at 50°C ambient and +/-4.5V supplies, if the current is 250 mA instead of 10 mA ; will leakage still be around 2 nA max...)

-I am also confused because the ADG1606 allows more current at +12/-0 V operation than it does at +/-5 V ; The ADG1608 allows more current at +/-5V than it does at +12/-0V.  I can't really see how their typical performance characteristics differ, so I don't understand why there is a difference.

 

 

 

 

Thanks in advance for your answers!

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