Hello,
Per the TPS7A7100 datasheet (page 17 - INPUT CAPACITOR REQUIREMENTS):
"In addition, simple usage of large input capacitance is known to form unwanted LC resonance in combination
with input wire inductance. For example, a 5-nH inductor and a 10-μF input capacitor form an LC filter that has a
resonance at 712 kHz. This value of 712 kHz is well inside the bandwidth of the TPS7A7100 control loop."
...
"The best guideline is to use a capacitor of up to 1 μF with well-designed wire connections (PCB layout) to the
upstream supply."
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The above statement leaves much to the imagination, we have four 100uF (MLCC 1210) caps and eight 22uF (MLCC 0805) within 500mils to 1 inch of the TPS7A7100's input pin. These MLCC capacitors are all on the top side of the PCB along with the TPS7A7100 and connected with a 2 inch wide copper plane. We would then place a 1uF (MLCC 0402) cap directly at the input pin as recommended above.
Any more knowledgeable souls who could confirm whether this will be OK or not? How close can additional MLCC based bulk decoupling be located?
Of all the TI linear regulators datasheets I've read, I don't remember ever seeing such a open ended warning on input caps...
Thank you,
Chris
