hello everyone,
i'm facing with very annoying ripple problem.
I have two LMZ14202H modules in my circuit design, both of them gets 28v input.
one is configured for 12v, and the second for 9v
when I measure the Vin and Vout DC characterization the results are ok
but, for AC I'm facing with very high ripple voltage (without load and with load of 0.5A).
I tried to fix this problem by:
1) adding more capacitance in the input and the output.
2) wire the GND from the input and output capacitance directly to pin 4-GND
3) changing the Cff cap for 0.018uF
4) adding 2x10uF with 2ohm res in parallel to the input capacitor (dumping circuit)
none of the actions that I mentioned above fixed the problem.
important to say:
1) this problem occurred in both modules.
2) I followed the exact measuring guide ( in this link: http://e2e.ti.com/support/power_management/simple_switcher/w/simple_switcher_wiki/2243.understanding-measuring-and-reducing-output-voltage-ripple.aspx)
3) this circuit designed exactly as in the application note of the datasheet
attached to this post the scope waveform, the DSN file and photos of the layout.
Please I need your help to fix this.
Best