Author Topic: Boost converter at low current  (Read 191 times)

0 Members and 1 Guest are viewing this topic.

Offline ubbut

  • Regular Contributor
  • *
  • Posts: 89
  • Country: de
Boost converter at low current
« on: June 15, 2021, 07:20:12 pm »
Hi,

for a project I need to convert 12V to 15V at relatively low output current (10-50mA). Usually my go-to switching controller is the AP3012. Low cost, high frequency.
However as it turns out at such low currents, the AP3012 has far worse ripple as compared to higher currents. The reason seems to be, that the 3012 goes into "pulse skipping" mode, effectively lowering the frequency significantly and thus creating a large output ripple.
I also tested the LT1615 with basically the same results.

Looking for an alternative part designed for lower current I found the LT1615-1, but even before the supply shortage it could not be obtained.

I did have success with LT3460, it is however much too expensive for my application.

AP3015 seems to have a undefined, much lower operation frequency. Have not tested yet

So basically this results in my 2 questions:

(1) Are there alternative parts I could use? Something I am not aware of? Recommendations?

(2) Is it possible to somehow reduce the ripple of the AP3012? I tried altering the feedback network, reducing and increasing the inductance and output cap - all with little to no positive effect.

thank you!
 

Offline evb149

  • Super Contributor
  • ***
  • Posts: 1838
  • Country: us
Re: Boost converter at low current
« Reply #1 on: June 15, 2021, 07:25:39 pm »
Of course the "brute force" inelegant option is to convert to say 17V and use a LDO to convert the noisy DCDC output to a quieter linear regulated output.

Though considering that it will be relatively compact, relatively low cost (you can use your favorite low-er cost boost converter and your favorite low-er cost LDO), it may win out over some more elegant "all in one" quiet supply solutions.

 

Offline SiliconWizard

  • Super Contributor
  • ***
  • Posts: 6850
  • Country: fr
Re: Boost converter at low current
« Reply #2 on: June 15, 2021, 07:38:00 pm »
I can suggest the TPS61099, or equivalent in the same series.
 

Offline evb149

  • Super Contributor
  • ***
  • Posts: 1838
  • Country: us
Re: Boost converter at low current
« Reply #3 on: June 15, 2021, 07:38:06 pm »
Why not check this out:
https://webench.ti.com/power-designer/

Just putting in the parameters of ~11V-13V in, 15V out, 20mA nominal output current, 50mA max. output current, 0.05% * Vout ripple, prioritize low cost give some first-glance reasonable options.  You'll have to drill into the data sheets and simulations to make sure it is well behaved and quiet over the whole range of I/O voltages and load currents.

One such option is LMR62014X.

 

Offline harerod

  • Regular Contributor
  • *
  • Posts: 172
  • Country: de
  • ee - digital & analog stuff
    • My services:
Re: Boost converter at low current
« Reply #4 on: June 15, 2021, 07:58:20 pm »
Hi ubbut, I think you are on the right track. The "pulse skipping" is to counter saturation of the inductor due to low load current. The minimum required load current depends on inductance and lowest duty cycle. AP3012 Figure 9 shows 20..90% duty cycle.
Caveat: Higher inductivity may result in a more sluggish response to changing load current.
Regarding a feasible component - just have a look at the distri sites, what's available today... Digikey has some LT1930 in stock.
I second EVB149's LDO recommendation. While supply ripple current is low for boost topology, output ripple is high. Depending on your application filter+LDO might be indicated.
« Last Edit: June 16, 2021, 05:37:03 am by harerod »
Before you speak, let your words pass through three gates: At the first gate, ask yourself “Is is true?” At the second gate ask, “Is it necessary?” At the third gate ask, “Is it kind?” – Rumi
 

Online Weston

  • Regular Contributor
  • *
  • Posts: 120
  • Country: us
Re: Boost converter at low current
« Reply #5 on: June 16, 2021, 02:57:09 am »
I cant think of any specific boost converters that fit your application off-hand, but the feature you want is "forced-PWM" mode, which means that the converter will never enter pulse skipping mode, regardless of load current.

Often dc/dc converters will have part variants that are always in forced PWM mode, or they have a pin you can tie to the supply / ground to define the behavior.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf