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I use an LMZ14201H in a certain circuit with the following parameters:
Iout: 600mA (max)
For some reason we have a peak of Radiated EMI at 70MHz approximately.
Are there any known issues or solutions?
We had in the past serious problems with conducted noises in low load conditions, due to the DCM/CCM transitions, we solved this problem, but the 70MHz radiated is hard to explain.
We're looking into this right now and will have a reply for you soon.
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In reply to Anston Lobo:
In reply to Emanuel Marinescu:
Here is the circuit and PCB layout
A few explanations skipped:
C15 is a tantalum capacitor.
This is the second revision of the circuit, we use the LMZ series in many applications with similar setup and layout, never had such issues.
This circuit requires an extremely low standby current and the load can go down to 10mA.
As mentioned, we had conducted emissions issues in the low load and took certain measures to avoid this, among other things the addition of the common mode choke, low frequency ferrite beads and increased increased capacitors.
The old setup used the LC filter recommended but if compared to the one above used only C6, C7, C9,C10,C11 and I1.
The evident 70MHz peak close to the allowed limit showed also there, barely passing the test but the CE wad bad.
The CE is the reason we keep the frequency around 330KHz.
These were the results of the old version:
The 68MHz is there and so another peak at about 330MHz. There is a raise also at 150MHz, quite small but needs attention, see below.
The new version passes quite well the CE test, but still gives the peaks now at 150MHz and 300MHz.
The customer requires testing the operation of 2 units (each in its own housing, totally separated)
When testing 2 units everything is amplified and fails. Here we can see the 70MHz back and big, at 150MHz completely fails and at 300MHz avery big peak.
Quite strange behavior, we never expected noise in this range and in fact based on many projects with the LMZ series we newer observed such high frequency noise. In fact we were very happy with the success we had filtering the clock from the CE tests almost completely.
I will really appreciate your assistance.
Can you set the frequency of one of the two converters to a slightly different frequency? If the two frequencies are set at least 100kHz apart, they will not add together in quasi-peak mode in the spectrum analyzer.
In reply to joe baldwin:
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