LMR16030: Voltage crashes momentarily at the output.

Hello

There are several possibilities.

1. What input voltage are you using for the test?  Make sure that the input voltage is not falling too far during the load transient.

2. How much current load do you see when the transient occurs?

3. Can you test with a resistive load to 3A and see if the output is stable.  Then step the load from no load to 3A and see if the output is OK.

4. This device is rated for a 3A load; more load will cause the output to fall out of regulation.

5. If all of the above is OK, then you may need more output capacitance or some adjustment to the feed-back compensation.

Thanks

Hi Frank,

1. I drew the schematic for 24V input, but in my test today, I applied 12v input voltage. I am giving the input voltage from the power supply.

2. Output crashes around 140mA with 12V input input. This event takes about 4ms. (device turns on, starts normal operation and crashes. again and again)

3. I tried this situation as follows before: I connected a constant load to the output as a resistor, tested about 5.25V, 2.5A constant draw. I was seeing a stable 5.27V without load.

4. It is suggested to use with raspberry pi max 5.25V, 2.5A adapter. which is below 3A.

5. How can I follow a path in this regard. If you want I can share the layout or whatever you want.

I am waiting for your precious returns. Can you help me solve this problem?

Regards,

Mehmet

Hello

If the regulator works OK with a static load of 2.5A, that is a good sign.

It may be that the Pi is drawing more current than anticipated.

You can test the Pi with a bench supply to see if it draws any surge current, etc.

If you can send your PCB layout, that would be helpful.  Altium is ideal; otherwise just plots of the layers and designators.

Thanks

Hi Frank,

I fixed the problem, it is totally caused by my fault. That is, the power supply was 12V, 250mA, and when the raspberry tried to draw more, it could not be supplied from the power supply. That's why he was rebooting constantly.

But I discovered there was another problem. I will use these devices in the vehicle and my output voltage to raspberry seemed very unstable. I am sharing the oscilloscope outputs of this.

As you can see, the min and max values are very high, this fluctuation is in micro seconds levels, but how can I prevent these voltage fluctuations to keep my device safe.

I also share the images of my board layout.

Top layer

Bottom Layer

How can I solve the voltage fluctuation? I'm looking forward to your answer.

Regards,

Mehmet

Hello

It is a little hard to read the total voltage fluctuation from your scope cursors, however it looks like

some high frequency noise from the switcher.

Here are some ideas that might help:

1. Avoid using thermal reliefs on the power components, such as input, output caps and inductor and diode.

These should be solid direct connections to the planes.  This is also true of the PAD, pin #9.

2. You should place C10 and C4 directly near the device; rather than C2 and C3.  C2 and C3

can be farther away.

3. Try to change the route of the FB resistor, R1.  You should avoid running near the inductor or diode. 

More important this trace should be connected right at the positive side of either C7 or C8; not near the inductor connection.

4. The trace going from the BOOT pin to the boot capacitor should be a little wider.

Thanks

Hi Frank,

I'm starting to revise the pcb to implement what you say.

I also have some questions to clarify, in response to what you said.

1. here I am going to fix the first item but there was a suggestion that I should put thermal via under the IC in the datasheet and in the EVM, and that's why I did it. Is your suggestion to remove these vias, can you confirm?

2. Ok.

3. Ok.

4. Ok.

It was suggested that nothing goes under the inductor, so I did not pass a plane or path. Is this a problem?

Lastly, would you suggest I put another 47uF at the output?

Please say if there is anything else you want to add. I will quickly send it to the new pcb.

Regards,

Mehmet

Hello

1. The thermal vias are good; the thermal relief tabs are not.  You should have solid connections

to the ground planes as in the layout example. 

It is OK to have nothing under the inductor.

You can leave a place on the PCB for an extra output capacitor(s).  I would suggest a place

for one large and one small device.

Thanks

Hello

Here are more resources for measuring and reducing output ripple and noise.

Thanks

https://training.ti.com/understanding-measuring-and-reducing-output-noise-dcdc-switching-regulators

https://e2e.ti.com/blogs_/b/powerhouse/archive/2016/07/27/how-you-measure-your-ripple-can-make-you-or-break-you

https://training.ti.com/power-tips-measuring-vout-ripple-dcdc-converters

understanding_measuring_and_reducing_outputnoise_0.pdf

Hi Frank,

Thank you very much for the documents you shared and your fast feedback. I've reviewed all of these and revised my card and I'm sharing with you.

Top Layer

Bottom Layer

I had revisions like this, can you examine it if I ask? Is there any mistake or point I missed?

If there is no missing or error, I will send it to a new prototip. I am waiting for your reply. Thank you.

Regards,

Mehmet