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CrossTalk between 3.3V and 3V Power Supplies

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Vinnie90

Joined Jul 7, 2016
86
Hi everybody,

I have a analog/digital systems: the digital part runs at 3.3V while the analog goes between +3V and -3V. The main supply comes from an USB port which goes to a 3.3V LDO regulator (U11 in the schematic). The USB Voltage goes also to the charge pump (U10) to generate the dual supply. Everything is on a PCB.

Before soldering the charge pump I soldered the LDO and all the ICs of the analog part. The problem is that when I connected the USB power I see almost 2.3V at the +3V and 0.6V at -3V. All the ICs have decoupling capacitors (100nF) between 3V3 and ground and also between +/-3V and ground. I thought though I had something not properly decoupled:

- I added 47uF electrolytic at the input and output of the LDO....not a big change
- I desoldered every component that has a digital and analog supply....the voltage at +3V dropped to 1V and the voltage at -3V did not change
- as last resort I desoldered the LDO from the board and now I see 0V at the analog supplies.

What could cause the problem?
Thanks for the help :Dpower.png
 
V

Thread Starter

Vinnie90

Joined Jul 7, 2016
86
Right I thought maybe was going to be too much information since I also have the problem without any load. Anyway for completeness I'll attach the load for the 3.3V and the +/-3V ( the decoupling are at the bottom). But still the problem is that even without load and without the LM27762 (so no analog supply) I still see some voltage at the +/-3V only when I have the MIC5225 on the boardPicture1.png
 
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