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Output resistance and inductance of LMZ12002 and LMZ12003

Binayak Shrestha
Prodigy 100 points
Other Parts Discussed in Thread: LMZ12002, LMZ12003

Hi,

I am using both LMZ12003 and LMZ12002 to power my Altera Cyclone IV FPGA. While doing Power Distribution Network (PDN) planning for my high board design, I need to supply the output resistance and inductance of the VRM in my PDN planning tool. I searched the datasheets, but I am not able to find the data.

It is strange that such important parameters have not been stated clearly. Am I missing some indirect method from which we need to calculate that information?

Warm Regards,

Binayak. 

  • 0
    TI__Genius 10115 points

    The inductors internal to the module are shown in the application block diagram of the datasheet. For the LMZ12003 the inductor is 6.8uH and for the LMZ12002 the inducance is 10uH.  The inductor resistances are in the 30mohm range.

    However, I believe the output resistance of the module you are looking for is actually the closed loop output impedance.  For buck converters in general this zo ~ 1/gain up to crossover frequency of the control loop after which the impedance matches the impedance of the output capacitors.  The gain of a typical control loop is around 60db or 1000.  Thus the output impedance is around 1mV/A up to the crossover frequency. The crossover frequency of the module depends on the output capacitance and can vary from 100Khz down to  10's of Khz.

     

    Regards,

    Marc