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PTN78020W Output Capacitance

Jeff Halnon
Prodigy 30 points
Other Parts Discussed in Thread: PTN78020H, PTN78020W

In the data sheet (SLTS228B) on page 13 under PTN78020W/PTN78020H Output Capacitor it says " The minimum capacitance required to ensure stability is a 330 μF. Either ceramic or electrolytic-type capacitors can be used ".  Let's call this Ref1.  On the same page under Ceramic Capacitors it says " When placed at the output, their combined ESR is not critical as long as the total value of ceramic capacitance does not exceed 300 μF ".  Let's call this Ref2.  Tabls 5 shows recommended capacitors.

Problem 1:  The maximum capacitance specified in Ref2 is less than the minimum capacitance specified in Ref1.

Problem 2:  The recommended ceramic capacitrors of Table 5 do not meet the minimum capacitance specified in the "Output Bus" column of Ref1

I could use several 100 uF ceramic capacitors at different loads in my application but am concerned about the total capacitance.  The design may end up with 300 uF to 400 uF of bulk capacitance distributed throughout.

 

  • 0
    TI__Mastermind 38230 points

    Jeff:

    The PTN78020W can have on the output bus, a total of 300µF of ceramic  capacitors  to meet both  minumum/maximum output capacitance requirements .To prevent  formation of  local resonances,  do not place more than three identical  capacitor values of 10uF  or greater in parallel on the output bus. . The output ceramic capacitance total does not  include <10µF capacitors. A number or 4.7uF ceramics can be placed stratigically in other locations.  

    Tom