TPS61030 with ceramic output caps?

vrover

Other Parts Discussed in Thread: TPS61030, TPS63020, TPS61032, TPS56121

Hi,

According to page 15 of the data sheet, a 10 pF cap in parallel with R3 (FB resistor) is a good workaround for using ceramic caps. I wanted to find out if this is a known good fix.

My layout has 2 TDK C3225X5R0J107M caps. One right next to the TPS61030 and the other exactly on the other side. The via holes are between the cap and the VOUT pins. The ground is connected via a copper flood to the big pad under the TPS61030, and with vias, of course, for the cap on the opposite PCB side from the chip.

I did look at the TPS63020 as one forum posting had suggested, but I think the 61030 is a better fit overall.

I am using the TPS61030 with system 3.3V in and 5V@ 2A out.

I was going to use the TPS61032 but the data sheet recommends TPS61030 if I use ceramic output caps.

Comments?

Thanks!!

over 13 years ago

0 Chris Glaser over 13 years ago

TI__Guru**** 150820 points

I assume you are referring to this post: http://e2e.ti.com/support/power_management/non-isolated_dcdc/w/design_notes/tps61030-how-to-use-ceramic-output-capacitor.aspx

While it may be possible to stabilize the TPS61030 in some applications, customers have found that they need to get very tight tolerance inductor's and output caps to exactly know the loop's response and compensate for it, as this ap note shows: http://www.ti.com/lit/an/slva274a/slva274a.pdf For this reason, it is more economical to just buy a tantalum cap or add a discrete resistor in series with the ceramic to give it some ESR.

We do not recommend using the TPS61030 with ceramic output caps.

For your power requirements, it is the correct part to use, though the TPS63020 works also.

I split your initial question into 2 posts. You can find the answer to your PG question here: http://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/p/135475/487096.aspx#487096

0 vrover over 13 years ago in reply to Chris Glaser

Intellectual 280 points

Hi Chris,

Thanks for your help!

If I stick with the TPS61030, then it sounds like the best thing is to put an R in series with the output cap. Looking on Digikey, I find http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=WSLJ-.025CT-ND which is a Vishay/Dale 0.025 OHM 0.1W 1% 0603.

I picked this because the app note used 0.025 for the Ta cap and my TDK 100uFd C3225X6S0J107M ceramics (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=445-6016-1-ND) are only about 1.9 mOhm. TDK doesn't make it easy to find the ESR - you have to look at the Components Characteristics Viewer buried
in their web page, but I think I figured it right.

Is this what you had in mind?

Should I not bother with the 10 pF in parallel with R3?

Also, I was going to follow along with the app note and use the 2.2uH inductor. This seems to apply equally to the Ta and ceramic cases and provides the best stability.
I was going to use the Vishay/Dale IHLP2525CZER2R2M0, 2.2UH 8A, 0.020 ohm. http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=541-1008-1-ND

Does this all sound good?

0 Chris Glaser over 13 years ago in reply to vrover

TI__Guru**** 150820 points

I would prefer to go a little higher with the discrete resistor, maybe 50 mOhm. And please follow the datasheet typical circuits--a small 2.2uF ceramic near the device with the larger tantalum hanging on the bus.

Yes, the ESR of ceramics is essentially 0.

Also, remember that ceramics have a DC bias effect whereby their capacitance decreases as a DC voltage is applied on them. So, your 6.3V 100uF ceramic will likely only exhibit 50uF of capacitance at 5V DC. So, you need more ceramic to keep the total above the 100uF required by the IC.

I would recommend using the adjustable version with a small Cff, R3. You should take bode plots on the final configuration and do load transients to make sure it's stable.

The inductor looks fine.

I would highly recommend ordering our EVM, http://www.ti.com/tool/tps61030evm-029, and doing the above changes to validate your circuit under your operating conditions.

0 vrover over 13 years ago in reply to Chris Glaser

Intellectual 280 points

Hi Chris,

OK, 0.50 Ohm it is.

Thanks for the reminder about the DC Bias effect. It's pretty amazing how much the value derates.

I did have the 2.2uF right there where the eval board shows it.

I will see about getting the demo board. It is a little disconcerting how the boost regulators seem a lot more touchy than the bucks.

Two final (for now) questions:

a) why isn't the TPS61030/1/2 support included SwitcherPro?

b) does SwitcherPro generally take into account the ceramic cap bias degradation? I ask because I also plan to use a TPS56121 in another part of this same design (not connected in any way with the TPS61030 design. If it doesn't, then I need to change things there.

Thanks!

0 Chris Glaser over 13 years ago in reply to vrover

TI__Guru**** 150820 points

Well, 50 mOhm or 0.050 Ohm.

Your final two questions should be directed to the eLab forum: http://e2e.ti.com/support/development_tools/analog_elab_and_tools/f/235.aspx I'm not up to speed on what they do there.

0 vrover over 13 years ago in reply to Chris Glaser

Intellectual 280 points

Yeah, right..050. That's what I meant :)

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TPS61030 with ceramic output caps?