TMUX6234: analysis of anomaly

What resistance are you measuring between the D1 and S1A/S1B pins?

C80 will keep the old charge. I'd guess that there is no problem with the switch itself. Can you show an oscilloscope trace of the relevant pins during switching?

Hey Rhea,

I'll double up on Clemens response here and ask for some waveforms to help better understand the issue.

Can you also help clear things up on my end?
You say CTRL2 is 0, VDDA=VDDA2=13.5V. So here it looks like you've directly supplied 13.5V to D1 so if you're measuring it relative to ground, you should see 13.5V, which is what you're seeing.
The 2nd case is this : "the voltage measured at D2 pin1 is 20V" a typo? D2 pin1 should be D1 pin1 or are you actually measuring 20V on D2 that isn't connected to anything? 

What are they expecting to see in these conditions? It sounds to me like, if the second condition is a typo, they're applying a voltage on the pin, are seeing the voltage they apply, but are somehow surprised by it. I think it's more likely that I'm misunderstanding something here though, so some clarification and waveforms would help

Thanks!
Rami

Hi Rami Mooti1：

1.D1&D2 are diodes,not TMUX6234 pins，you can find them near U9 and U11.

2.VDDA1& VDDA2 are inputs，VDDA is output.

3.I hope，when VDDA1 is cuted off by CTL0_VDDA1，the voltage measure at C75 & C76 is zer0 ,not 20V. when VDDA2 is cuted off by CTL1_VDDA2，the voltage measure at C84 & C85 is zer0 ,not 13.5V.

Hello wangzengfeng,

Ah I see now, thanks for clarifying. The pins on the mux are also D1 and D2 and I got a little confused.
So it does seem that either something isn't working as expected with the DC/DC converter or some charge is being held somewhere. 

Could you try and remove the mux and see if the output of the converter behaves as expected? You may need to remove the some of those bus loading caps like C75,C76, etc. Just want to see if the output actually pullsdown when you only have the LP device operating alone.

You could also put a stronger pulldown on the D1 pin1 side and see if the charge is just being held in the caps and just needs to be dissipated.

Thanks,
Rami

Hi Rami Mooti1：

Thank you for your suggestions, I conducted two experiments and results as blewo:

1.Remove  C75 / C76 / C84 / C85,then turn off VDDA1 by CTL0_VDDA1 is low,turn on VDDA2 by CTL1_VDDA2 is high, the voltage measure at D1 pin1  is 20V;when turn off VDDA2 by CTL1_VDDA2 is low,turn on VDDA1 by CTL0_VDDA1 is high, the voltage measure at D2 pin1  is 13.5V.

2.Remove the mux，turn off VDDA1 by CTL0_VDDA1 is low,turn on VDDA2 by CTL1_VDDA2 is high, the voltage measure at D1 pin1  is 0V;when turn off VDDA2 by CTL1_VDDA2 is low,turn on VDDA1 by CTL0_VDDA1 is high, the voltage measure at D2 pin1  is 0V.

So I think  the MUX is causing this problem.

TKS ! 

Thanks for the update wangzengfeng,

So from condition one, it sounds like you're able to toggle on and off the control properly so it doesn't seem like the issue is there.

In condition 2 did you put the caps back in place or is it just the mux, with no capacitors? The mux itself is just a FET and will act as essentially a resistor with some parasitic capacitance as well. So the only source for the voltage there would from the dc-dc converter directly, the charge being held in the caps, or the third possibility would be maybe some ESD path. What's the VGHM voltage (VDD on the TMUX6234)?

Also, how long does the anomaly last? Doe sit remain there indefinitely or does it go away after some time? Scopeshots of what you're seeing can help as well

Thanks,
Rami