Looking for high-voltage analog matrix multiplexers - Page 1
Forum section: electronics / projects

author: SiliconWizard
author_rank: Super Contributor
timestamp: April 17, 2018, 09:50:34 am
content: Hi all,I'm looking for analog matrix-like multiplexer ICs, typically for signals up to +/-15V, up to +/-30mA, 8x8 or 16x16 channels.Spec-wise, something like the ADG1438 would be a good fit. Unfortunately, to make an 8x8 matrix would require 8 of them (and a routing mess).I've found a lot of ICs, but nothing that really gets close to this kind of specs.If anyone can suggest any suitable part...Thanks!

author: Zero999
author_rank: Super Contributor
timestamp: April 17, 2018, 12:29:07 pm
content: Are you sure an analogue switch is what you want? 30mA is on the high side.

author: SiliconWizard
author_rank: Super Contributor
timestamp: April 17, 2018, 01:48:22 pm
content: Well, yes. What would you suggest?The reference specs I'm targetting, the ADG1438, are fine. Those are specified at 169 mA per channel at 25°C.

author: jbb
author_rank: Super Contributor
timestamp: April 18, 2018, 07:23:36 am
content: Well, if you need the full NxN then you will need N2switches. Which starts to suck really fast.For N = 16, that's 256 switches. Which will cost you a pretty penny.Do you need all the pins at the same time? It might be possible to use an intermediate bus and subdivide the problem (which can help a lot where polynomial difficulty - i.e. N2- is involved).

author: BrianHG
author_rank: Super Contributor
timestamp: April 18, 2018, 07:43:20 am
content: Quote from: SiliconWizard on April 17, 2018, 01:48:22 pmHmmm, you want 30ma across the ADG1438 21 ohm on resistance per switch = 0.7v loss = 21mw of heat. Multiply that by 8 for sinking 30ma on 8 switches simultaneously = 168mw total dissipation. Note that with a +/-15v supply, the on resistance drops to 10 ohm as you reach the rails & keep the IC at room temp. Expect 20 ohm at 85 degrees. I would say if you use the chip to 30ma/channel on all 8 channels simultaneously, add a small IC heatsink to play it safe.Run the IC at full 169ma on all 8 channels simultaneously and it will cook without a big heatsink and some forced air cooling radiating a full watt or more. And, as it warms, the internal resistance per channel rises as well, accelerating the effect.

author: SiliconWizard
author_rank: Super Contributor
timestamp: April 18, 2018, 01:54:03 pm
content: As the structure of the ADG1438 (which is fine for my requirements) is a multiplexer, it means that the overall current will be divided amongst all the channels that are ON, since there is a common end. And I don't intend on having more than 30 mA max distributed to 0 to 8 outputs. I can guarantee (with the way the switches will be configured) that there will be +/-30 mA max per current path. So the limitation is fine with me.As I said, a single IC that would basically integrate 8 ADG1438 would be perfect. I can do this with 8 chips, but it's a cost and huge real-estate waste.I've found such matrices (often called 'crosspoint arrays') but usually with much higher Ron resistance (in the order of 100-200 ohm) and/or lower max voltage (such as 12/13V max, whereas I'd need up to +/-15V), such as the AD75019. With lower Ron, it would be almost perfect (I could live with +/-12V max if everything else fits).