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Question about circuits parameters of TPS61040/1

Bobby10579
Prodigy 10 points
Other Parts Discussed in Thread: TPS61041, TPS6104XCALC, TPS61040, TPS61080, TPS61170

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

  • 0
    TI__Guru**** 152426 points

    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.