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Design >> High-Power Design >> Buck separate ground substrate coupling meas
https://designers-guide.org/forum/YaBB.pl?num=1171970232

Message started by Matthieu on Feb 20^th, 2007, 3:17am

Title: Buck separate ground substrate coupling meas
Post by Matthieu on Feb 20^th, 2007, 3:17am

Hi all!

I am currently designing a buck DCDC converter (I have already received the first silicon). During design, power and command ground have been separated in order to minimize noise on command side circuit. The DCDC oscillate in some cases at about a 1/8 of switching frequency. I have tried to reproduce this behaviour in simulation and I now think oscillation are due to the bandgap ground coupling with power ground (a few mV of noise on bandgap ref generate oscillations).

I have tried to measure substrate coupling of the two grounds but I am not sure if the method is valid. As there silicon already exists, I have simply used a ohm-meter to mesure the resistance between the two ground. The ohm-meter injects 1mA and mesure the voltage. I have found about 16 Ohm of coupling. This mean there is 16mV between the two ground while measuring, it seems like the same conditions as when circuit is running (junction bias).

Do you think the method is valid?

Matthieu

Title: Re: Buck separate ground substrate coupling
Post by ACWWong on Feb 20^th, 2007, 9:08am

yes, using an ohmmeter will tell you the DC impedance between the grounds... which will also be valid for low frequencies.
cheers
aw