We are using the LMZ10504 module in application where the Output load capacitance can vary from 22uF to 220uF.
We need to ensure the stability of the module other all the output capacitance range, with the same values of compensation. To establish an optimized compensation stage, we need to know the values of the internal compensation network included in the LMZ10504.
Can you please provide us these values? The AN2013 presents some curves, but it is impossible to use it, as we don't know on which component (LMZ1050x) and power stage it has been done,
Thanks for your help.
The internal compensation for LMZ1050x family is the same. The curves for the compensation stage gain and phase in AN2013 can be used. The power stage transfer function should be with your desired output capacitors.
To cover the wide range of output capacitors, one way is to design two sets of compensations for the two extreme cases and cross check each other for stability. Pick the one that is stable for both extremes. Case with extreme ESRs should also be checked.
For the LMZ10504, it should be safe to design for the 220uF output capacitor. The control loop would be slower for the 22uF output capacitor, but it should be stable. Carefully place the high frequency pole based on the ESR values the output capacitors may have.
Thanks for this first answer. To optimize the compensation, with 22uF and 220uF ceramic capacitors, the best way is to check therocally the complete loop of the dc/dc. As there is an internal compensation, I need to know some parameters : at least value of the internal resistor in the compensation stage. It is difficult to use the curves of the AN2013, as we don't knwo for wich values of Rfbt, Ccomp they have been done, and for whcih value of the power stage (Vin, Cout).
All these information are of great interest to optimize the compensation network.
The compensation components are as follows:
internal Rcomp = 200kohmsinternal Ccomp = 90pF (in series with Rcomp)
Hope this is helpful.
Thanks for the answer, but I don't understand the values. According to the AN2013, the LMZ10504 has an internal compensation (Zero) at 17.6KHz. With the value you give, the internal compensation is at 8.8KHz (F=1/(2*PI*R*C)).
Can you check and tell me where is the misunderstanding.
You are right. I made an error in giving you the numbers. The resistor is actually 100K. This makes the frequency to be as follows:
F = 1/(2*PI*100K*90p) = 17.683KHz
Thanks for the answer.
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