Hi Excellent Ti Guys,
I build a circuits boot the +5V input from USB (after hot-swap) to +/-15V output with TPS61041.
But I it's output ripple (voltage ripple) is very high, peak to peak valued over 1V.
Ciucuits like picture up shows, and output are filter by circuits like below shows:
L1: 10uH; R1: 140k; R2: 12.1K; CFF:47pF;
I try to modified L1 and Cff as datasheet described but nothing improve.
Some formula have offered in it's datasheet, but they all have no units, I also use the tools link below for parameter calculation.
http://focus.ti.com/docs/toolsw/folders/print/tps6104xcalc.html
but it's result conflict with the datasheet shows. So, I am confused about how to reduce the output ripple to the value I want. (Example: 10~15mv).
Could you offer me some suggestion?
Thanks.
Bobby
The TPS61040 is a hysteretic converter and so needs a minimal amount of ripple for operation. I have never seen it operate with less than ~50mVpp of ripple. To reduce the ripple, you will need the smallest inductor value to give you the maximum 1MHz switching frequency and a large ceramic (or other very low ESR) output capacitor. You should be able to reduce the ripple with a post output filter, similar to what you have shown above but the filter will need to have a roll off point at least 1 decade below the switching frequency.
If this doesn't work, then try moving to a TPS61080 or TPS61170. Figure 25 of the TPS61080 datasheet is your application.