DC-DC with very low output voltage ripple

We need DC-DC (Vin = 12V, Vout = 0.9V, 6A) with voltage ripple allowed (peak to peak , 600 KHZ TO 20 MHZ) is 2 millivolts.
Could you recommend best solution (DC-DC part, output additional filter and so on) for that?

Thank you in advance

Apologies for the delayed response.
We have the following 2 parts which nearly matches your required specifications:
1)MPM3683-7:- This part has an inbuilt inductor and the maximum allowable switching frequency is 1.15Mhz.
2)MPQ8623:- This part has the switching frequency that goes till 2Mhz. The output filter for your application with this part that can be used is L=1.2uH and Cout=80uF.

Let us know if this works.

Yash Shah