TPS62113 - singing/whining inductor problem.

This kind of noise from the power supply can usually be fixed with external component selection.  Thank you for posting a schematic but it is unreadable as it is too small.  Could you re-attach a pdf?

If you need the enhanced LBI version, then this is likely your best IC but I just wanted to let you know that we released several replacements to the TPS62110 last year: TPS62140 and TPS62160 and various current limit options.  We also have the brand new TPS62125 which does have the LBI function essentially.  I would recommend these newer ICs.

Thanks Chris,

The LBI is not important, but the design was made so that any of TPS62113/TPS62110/TPS62111 could be dropped in depending on inventory availability.

This is part of an intrinsically safe device, so the requirement of the resistors and crowbars are a requirement.  Also I am not able to increase the inductance on the board or the capacitance at the input of the buck.

Hopefully this pdf version will appear better?   Let me know if it is still not clear.

0511.tps62113 sch.pdf

Your safety requirements are understood.  Since you're not using the LBI function, I would highly recommend that you use one of the newer devices that I mentioned.  The control method is better and they allow for smaller external components.  They also have multiple device versions available, fixed and adjustable.

I would need to see waveforms of Vin, SW, and Vout to comment further but it is likely that you have too much source impedance--too much R and not enough Cin.  Do you have to have all that Cout?

One other thing:  You might check your load current.  Is the load changing from light to heavy load at an audible frequency rate?

Hi,

I took a look at the newer devices, but require the high input voltage range.  The TPS62125 is close, but doesn't deliver the maximum current that could be expected -- short 600 mA bursts from a radio, as well as powering a 12V boost with a 60 mA load. 

The extra Cout was to reduce the ripple (requirement is less than 50mV requirement from our radio chipset).  I tried remove 100uF off of that, but it didn't impact the noise.  In fact, I am wondering if it is coming from the inductor.  I examined it a bit closer and it could be coming from the buck itself.

I have some quick pics snapped from the scope.  I can upload better ones if these don't provide sufficient info.

VIN

SW

VOUT

These waveforms are sufficient.  What is the frequency of the SW node?  The IC is likely operating in the audible range due to your light load.

Removing a lot of your Cout or operating the IC in forced PWM mode should eliminate the issue.

I'm not sure about your comment on the input range of the newer devices.  The TPS62140 and TPS62160 have the same 3V-17V range as the TPS62110.

Hi Chris,

Sorry I will have to check out the frequency on Monday.   I incorrectly typed in TPS62040 and TPS62060 when looking at the parts.  I see you're correct about the input voltage range.

What are the distinctions between these parts at the TPS6211x series?  I thought this series was fairly new, is it being discontinued already?

Thanks,

Warren.

Also...

As far as operating in the audible range under light loads, is there anything to worry about, aside from the generated noise somewhat disconcerting?

No, there is no issue with operating these devices with audible noise.

The devices I mentioned are simply next generation high Vin buck converters.  The TPS6211x is not being discontinued.  In fact, we discontinue very very few parts--none that I can think of.  I just wanted to make sure that you were aware of the newer parts as they offer more capabilities, better performance, and smaller solution size.

Hi,

If the TPS62140 is a drop in replacement, I will give that a try.  It would beneficial if I could drop the inductance and capacitance of the whole circuit for other reasons to do with certification requirements.

As far the inductor audible noise, if I reduce the capacitance, I found the ripple was too large when the load increased to 600 mA for the radio bursts.  If the audible noise is not a real problem, I am happy to leave it alone, but I did want to make sure it was not a symptom of a problem with the circuit.

Is there a good rule of thumb for choosing Cout with switching supplies?

Every switching power supply is different, so you must follow the datasheet's recommendations for the output capacitance.  For the TPS62140, there is also an app note on optimizing the output filter that can be found on the product page.