DG419 switching issues

[Merlyn]

Hi,

I decided recently to use 2pcs of DG419 to make a DPDT switch and I got some weird things going on.

https://www.vishay.com/docs/70051/dg417.pdf

The DG419s are powered from a single rail supply (9V). As per datasheet V- (pin7) is connected to GND (pin3) and VL (pin5) to V+(pin4).
First weird thing is at around 400mV RMS (1kHz) the DPDT switch would start passing signal even when  not powered.
Second when powered at around the same level it would start clipping while according to datasheet it should pass levels up to the rail.
I haven't used these before and I guess I'm missing something.

[Benta]

If your signal is ground referenced, you're outside the operating range of the switches. If you can, DC bias your signal to 1/2 V_DD. If this is not possible, you need a bipolar power supply for the DG419s.

I've used the DG419 in a lot of projects, even real-time switching of analog video. They're great little devices.

[Merlyn]

Thanks for your input. I'll try that.

[Zero999]

There are analogue switch ICs which will work with negative signals, but they're typically only rated for 5V operation or less.
https://www.intersil.com/content/dam/intersil/documents/isl5/isl54059.pdf
https://www.st.com/resource/en/datasheet/stg5682.pdf
http://www.onsemi.com/pub/Collateral/NLAS2750-D.PDF

More information about analogue switches.
http://www.analog.com/media/en/training-seminars/tutorials/MT-088.pdf

[Merlyn]

I rewired the circuit and added a negative rail (via charge pump) and the headroom problem is now solved.
Not that it matters but the strange issue of the switch passing signal when not powered is still there.

[Zero999]

I rewired the circuit and added a negative rail (via charge pump) and the headroom problem is now solved.
Not that it matters but the strange issue of the switch passing signal when not powered is still there.

If the analogue switch is unpowered, then it's not surprising it's passing some of the signal, which will leak through the ESD protection diodes.

When the analogue switch it unpowered it should be disconnected from all signal sources. It is not the same thing as a relay.