LM4128 Cin

Steve Widener

Other Parts Discussed in Thread: LM4128

The LM4128 datasheet (revised April 2013) states on page 12 (Component Selection) that Cin must be > or equal to Cout. Does this mean that the nominal values are ok (1uF on the input 1uF on the output) or does it mean that the CAPACITANCE must be higher on the input vs the output (so 1uF & 1uF would not work due to tolerances of the capacitors)

over 7 years ago

0 Christopher Dean over 7 years ago

TI__Intellectual 1745 points

Hi Steve,

Correct, the LM4128 does require Cin >= Cout. If the capacitors will be de-rated in the application due to DC bias or temperature, or there is concern about the tolerance of the capacitors, I would suggest adding a little more Cin to remove doubt about the capacitance. Perhaps adding a 0.47uF, or using a 2.2uF Cin if you want to stick with a single component.

Sorry for the long delay, I am acquainting myself with this new forum.

Chris

0 Steve Widener over 7 years ago in reply to Christopher Dean

TI__Genius 9595 points

What happens if Cin < Cout?

0 Christopher Dean over 7 years ago in reply to Steve Widener

TI__Intellectual 1745 points

The Cin >=Cout requirement is likely to maintain stability across all specified operational conditions.

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LM4128 Cin