LMZ31506 6A SIMPLE SWITCHER

O'Connor%20Ed

Other Parts Discussed in Thread: LMZ31506

We are using two LMZ31506 6A SIMPLE SWITCHER® Power Modules that operate with 12VDC In and 5.5VDC at 4.2Amp Out and 5.6VDC at 4.5Amp Out. We are operating at 800 KHz switching frequency. These supply's are driving a synthesizer and RF circuits. We see the 800KHz switching spurs on the RF signal from the synthesizer. I did an experiment using power supply signals wired from a second board to a first board with the power supplies removed. The spurious signals when away. This leads me to believe that I have ground currents from the power supply's getting into the synthesizer. I want to isolate the power ground from the synthesizer and RF circuits ground. How should the power supply outputs be connected? Should filters be used for the ground connection?

over 7 years ago

0 Arief Hernadi over 7 years ago

TI__Mastermind 23815 points

Do you have the layout picture of the device? The switching currents is normally circulating around the input capacitor. Therefore you want to put the input capacitor very close to the IC.

You can also use an EMI filter design in application note an-2162

7875.EEOL_2012MAR29_POW_AN_01.pdf

0 O'Connor%20Ed over 7 years ago in reply to Arief Hernadi

Prodigy 20 points

I want to separate the ground layer of the power supply from the RF ground layer of the RF circuits the power supply is driving. I intend to connect these grounds at a single point. Should the single point connection be filtered with a choke or ferrite bead to limit high frequency power supply spurious ground current.
Ed O'Connor

0 Alan Martin over 7 years ago in reply to O'Connor%20Ed

TI__Expert 4365 points

LMZ31506_Example_Sch.pdfArief asked me to illustrate the nest method to do this. Attached is a schematic and views of each layer for best performance.

The key is placing the adjacent capacitor pairs as close as possible. Create capacitor footprints with two routable nets on each end cap. Drill 8 tiny vias in each end cap pad for connection to other layers.

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LMZ31506 6A SIMPLE SWITCHER