Hi James,
If you consider input filters for DC-DC converter inputs (not a must,
but a good idea), you want to have one filter for each converter input.?
In such a case if you design each converter with its own input filter to
be stable, there will be no problem.? I have been designing computer
systems with many DC-DC converters in the past 22 years (also up to a
dozen converter inputs connected together without input filters) and
there were no issues around this.? The key is not to save on high-ESR
bulk capacitors connected across the input of each DC-DC converter.? In
practice I have found the loop stability on the output side to be much
more challenging to solve, but that should be handled differently.
You can find a few additional considerations in
http://www.electrical-integrity.com/Paper_download_files/DC12_11-MP2.pdf and
http://www.electrical-integrity.com/Paper_download_files/DC17_PAPER_11_OverviewComparisonPowerConverterStability_Hartman.pdf
Regards,
Istvan Novak
Samtec
On 6/4/2019 3:45 AM, James Pawson (U3C) wrote:
Morning all,
I?m designing an EMI filter for a DC input power line that has four
DC/DC converters all running off it.
I know that the output impedance of the EMI filter needs to be much
lower than the input impedance of the DC/DC converter to prevent
oscillation/instability. But what happens when there are multiple
DC/DC converters running in parallel from the same input? How do the
input impedances interact? Do they appear in parallel or do the
control loops isolate stability issues to individual converters?
My understanding from this paper -
http://www.ti.com/lit/an/slua929a/slua929a.pdf - is that the control
loop and output filter of the DC/DC contributes to the stability
analysis. If so, then *each DC/DC can be considered individually* with
the filter being designed to have margin to the lowest input impedance
of all of the converters. This is instead of just adding all the input
impedances in parallel.
Is my understanding correct?
Thanks in advance,
James
James Pawson
EMC Problem Solver
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