LM5161: LM34940 inductance gear whine

Lina Wang

Part Number: LM5161
Other Parts Discussed in Thread: LM34940

hi TI,

Remark, I can't fill LM34940 part number in above part number, so use LM34940 to replace.

I Have one customer used LM34940, which they find their output inductance have gear whine, and this schematic as below.

and they have used two brand inductance, one is MAPM0630F, another is KMPH0630, and KMPH0630's gear whine is lighter than MAPM0630F.

could you help to improve it? and could you tell us, what's reason will lead to this gear whine, thanks.

over 6 years ago

0 Ambreesh Tripathi over 6 years ago

TI__Expert 6860 points

Lina ,

It seems like the device switching is not stable . Can you please share the Switch node Waveform as well as Layout of the design . Also customer can try reducing the resistor R119 from 499k to 250k to increase the ripple injection on the feedback .

---Ambreesh

0 Lina Wang over 6 years ago in reply to Ambreesh Tripathi

Intellectual 960 points

https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/waveform-test.7z

0 Lina Wang over 6 years ago in reply to Lina Wang

Intellectual 960 points

Ambreesh,
sorry for reply later, last attach is Waveform and layout picture, pls help to check it, customer wait for Mp, so they want to know how to deal with it.

0 Ambreesh Tripathi over 6 years ago in reply to Lina Wang

TI__Expert 6860 points

Lina ,

What is the output load ? The switching waveform doesn't look stable .

Also there are many issues with Layout .

1. Input di/dt loop needs to be minimized ieHF bypass cap needs to be placed between Vin pin and the diode's anode .

2. Boot strap ,Vcc and FB components need to be placed closer to the pin .

3. the Ripple injection placement needs to also be modified as shown in typical layout above .

My recommendation is to evaluate the design on EVM and then use its Layout as reference for the board design .

---Ambreesh

0 Lina Wang over 6 years ago in reply to Ambreesh Tripathi

Intellectual 960 points

hello Ambreesh,

thanks for your comment, their output load is 10-60mA.

so, whether is this part have PFM mode lead to this issue.

0 David Baba over 6 years ago in reply to Lina Wang

TI__Mastermind 40040 points

Hello Lina,

I am not able to open win rar files. Based on comments made above, it looks like the layout maybe the issue? Not sure what your question is above, can you please rephrase? Also, did you try to order an EVM?

Thanks.

David.

0 Lina Wang over 6 years ago in reply to David Baba

Intellectual 960 points

hello，

could you help to check the customer 's whole lay file and some of wave.

pin 11 wave

pin 12,13 wave

0 David Baba over 6 years ago in reply to Lina Wang

TI__Mastermind 40040 points

Hello Lina,

I checked the layout and I agree with Ambreesh's comments above. There are many things concerning with the layout. I would ask the customer to obtain and EVM to compare results and give customer more confidence in the need to change the layout that closely follows above and EVM.

Sorry. I hope this helps?

Power management

Power management forum

LM5161: LM34940 inductance gear whine