I have a power supply board that supplies a DSP, FPGA, CPLD and other components of a system. When I measure the resistance between power rails and GND using a multimeter I get the following readings:
- Between 12V and GND: Infinite
- Between 5V and GND: Infinite
- Between 3.3V and GND: 250 Ohms
- Between 1.2V and GND: 40 Ohms
The 3.3V and 1.2V rails have many decoupling caps around power supply pins of the DSP and FPGA, are they the only cause for this much reduced isolation between these voltages and ground?
Is it safe for the long run to work with these specs? The system is now running perfectly.
Also how can I avoid this issue in future designs?
In a project I'm currently working on, one of the tests that will be done on the product will be isolation tests. The customer will measure the resistance between supply rails and ground and want it to be greater than 10 Mega Ohms, that's why I want to avoid these low resistance values. Is there a device used to measure isolation? or it's done with a normal ohmmeter?
These measurements are done when the system is powered OFF.