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Hi Mike,The melted pins almost sounds like the chip latched up. Really has me puzzled. I wonder if the action of pulling the cable caused something like switch bounce. But would switch bounce unleash huge current spikes? To melt the pins implies large currents for appreciable amount of time which leads back to a latch up condition maybe a supply decoupling cap was large enough value to hold a charge. Was there a minus voltage on the board ? I'm sorta just thinking out loud
How were your psu remote sense terminals connected?
The melted pins almost sounds like the chip latched up. Really has me puzzled. I wonder if the action of pulling the cable caused something like switch bounce. But would switch bounce unleash huge current spikes? To melt the pins implies large currents for appreciable amount of time which leads back to a latch up condition maybe a supply decoupling cap was large enough value to hold a charge.
Was there a minus voltage on the board ? I'm sorta just thinking out loud
Hi Mike,
I am considering a problem with the ground connections. Do you think that if the analog and digital grounds got separated that the MAX9611 chip would self-destruct. My feeling is that it would.
spec
Well that is good news Max- glad you got the circuit working.I have an update. I just got a few more of the MAX9611 ICs in the mail this morning and tried to recreate the problem. I was unsuccessful.
I tried it both with and without a TVS diode installed across the power supply output rails. No smoke. Maybe it was a defective part, or a really smart intermittent problem.
I suppose I can call off the dogs at this point. What I was mainly trying to get out of this thread was a sanity check and that there wasn't anything big I was failing to realize.
Thanks everyone for taking a look at this for me.
I was going to suggest making it zero ohms. Albeit the installed resistor is a small value, there will still be noise dropped across it, which may or may not be a problem in a mixed signal design.Well that is good news Max- glad you got the circuit working.
Can I make a suggestion which is completely emotion rather than science: change the resistor coupling the digital and analog grounds to a through hole half watt or higher component or other more substantial resistor than surface mount. I have a phobia about grounds- sorry.
spec
I think you misunderstood me, I meant are you using a bipolar design? i.e. +V/-V,.Possibly. Unfortunately, I have no way of knowing at this point. I'm not sure where a reverse voltage could have come from. The load is just a big power resistior.
Yes, agree zero ohms would be better.I was going to suggest making it zero ohms. Albeit the installed resistor is a small value, there will still be noise dropped across it, which may or may not be a problem in a mixed signal design.
Can I make a suggestion which is completely emotion rather than science: change the resistor coupling the digital and analog grounds to a through hole half watt or higher component or other more substantial resistor than surface mount. I have a phobia about grounds- sorry.
I think you misunderstood me, I meant are you using a bipolar design? i.e. +V/-V,.
What I was thinking the problem may have been was that the power supply regulation went from 2 ohm load to no load, thus the supply output momentarily increased above the 48Vdc, and perhaps exceeded the max volt in on the chip thus causing a latch up condition in the parasitic PN junctions of the device (Purely guessing mind you, but you may be able to check with a good digital scope triggered on the DMM disconnect).
I have wondered for a while whether or not I was doing this properly. Several years ago when I was working on my first mixed signal design, I searched for a reference or some good rules of thumb on how to separate ground planes. I remember there not being a lot of clear direction out there on this topic, or maybe I just didn't know what to look for. I can't remember how exactly I settled on the 0.1 Ω resistor, the 100 nF cap, and the 1 uF cap all in parallel. But, my goal was to minimize noise in the analog portion of the circuit, and for that purpose it seemed to work pretty well for me in the past. Admittedly though I didn't do a lot of experimentation with alternate configurations so I wouldn't be shocked in the least if this arrangement isn't ideal.
I can replace the 0.1 Ω resistor with a zero Ω one as you and Mike suggest. That's no problem. But that sort of leaves me with the question about what to do with the caps. Are they doing anything for me here? What would you think about simply removing them?
Also, what if I omitted the zero Ω jumper and just replaced it with a trace connecting the ground planes instead?
???This thread got lost somewhere.
Oh I see- I miss points in previous posts all the time. It is a kind of word blindness (laziness too on my behalf).Not following from the beginning made the thread difficult to follow. I just added my relevant $0.02 USD to the discussion. Cooking and eating for the recent Holiday took priority.
Hi VNE,
So after all that, yes, I would advise joining the digital and analog grounds on your circuit by a solid conductor, but only in one place to avoid ground loops. Obviously, you can then ditch the capacitors that you mentioned.
Connect SET to 0V and leave OUTPUT unconnected. In general, all inputs of an integrated circuit should be set to a defined state or they may assume any voltage and cause weird effects.[the question] has to do with the MAX9611, specifically what to do with the SET and OUT pins. Should I leave them floating?
I am not using the features of the IC that those pins are used for and I have searched the datasheet for guidance on what to do with them in that case but I've come up empty. Any thoughts?
Connect SET to 0V and leave OUTPUT unconnected.