LMR14030: High amplitude sawtooth at output

Hi Daniel. I put x6 10 uF capacitors and now it works. Thanks!

UPD. Unfortunatelly not. When jlink debugger was connected the power supply works fine with more capacitors. When I disconnect it the sawtooth appear again. I will make suggested measurements and return with results.

Hi,

I put 150 uF 50V electrical capacitor and it's still bad.

Here's the layout:

What waveform should I provide?

Thanks.

HI

below is some of my comments

1. the SW wire is long which may make the device coupling the noise from SW and don't let the VO feedback wire which is conneting to R8 rounting from the diode. try to fly direct from Vo to R8.

2. what is the votlage rating of C11 and C10, 16V or 25V ,can you try to add a electrical cap at output, if 16V cermaic, the DC bias of 12V will make the effective capacitor very small for 16V rating cap.

for the waveform , pls help check SW and SS with 20us/div, 

Thanks

Hi,

I've already put four 47 uF ceramic capacitors with 25V rating. Should I try an electrical cap anyway?

Here's the SW:

And SS:

Hi

yes, Pls try add an electrical capacitor 

I saw SS drop and SW is not very stable, not sure where the noise come from. can you try add a 470pF parrelling with R9 to filter the noise coming into FB.

by the way, can you try with eletrical load see whether the same issue come out?

Thanks

Daniel Li

Hi,

With electrical capacitor the sawtooth becomes smoother:

470pF capacitor doesn't change anything. With 4x10uF capacitors at Vin, 4x47uF caps at Vo and under the load, it works good.

Hi

glad to see it works. I will close this quesiton, if you have further question, you can reopen it.

Thanks

Hi,

but how to get it work without the load or if the load is minimum? I mean when the consumption is about 3 mA I see the huge sawtooth, but when the consumption is 4 mA it disappears.

HI

if 1mA, simple way is reduce the divide resistor value to get 1mA load, how huge of the sawtooth? from EVM, it is 50mV level with proper capacitor. is it constant 3mA or the average load is 3mA?  can you check with output current waveform?

Thanks