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LMZ21701: output capacitance

Yuri Bykovtsev
Prodigy 10 points
Part Number: LMZ21701
Other Parts Discussed in Thread: TPS82130

Dear community!

I am working on a design with Zynq 7000 and our team decided to use LMZ21701SILT to provide stable power supply for +3.3V from +12V. PCB design guide requires to place several capacitors near Zynq power pins in total of 215uF. On the other hand, LMZ21701's datasheet says, that output capacitor should be in range of 10-200 uF, but says nothing (as far as i can see) about whole output capacitance. So the quiestion is can i use LMZ21701 if i place 100uF capacitor near its output pin and leave 215uF capacitance near Zynq, or i should use another DC-DC converter which has bigger allowed output capacitance characteristics?

Thank you for your help!

  • 0
    TI__Guru 50120 points
    Hi Yuri,

    It depends on the capacitors that you pick for the output. You would need to take into account DC bias effects at 3.3Vout. If you are using 100uF+215uF (whole capacitance), after derating at 3.3Vout it could fall within the 10-200uF range such that using the LMZ21701 in this application makes sense.

    Another alternative to this is the TPS82130. It is in the same package(uSiL) with a output capacitance range of 22uF - 400uF. The efficiency for 12Vin/3.3Vout at 1A is roughly 87% which is very close to the LMZ21701.

    Regards,
    Jimmy