LM61495: LM61495RPHR

Sorry i forgot VIN= 12V

Hi Timo, sorry to hear about the issue.

It maybe related to the stability of the converter. 

What is the voltage rating and case size of the output capacitance?

I would advise they capacitors be rated 16V.

Could you try increasing the voltage rating on the output capacitors to avoid them derating and possibly increasing the count if you are still running into issues?

Hi Marshall, many thanks.

My vin is 12-13.9V

I think my issue its by R1 the Rreset. Its 18ohm.

Wgat do you think?

What is the best R for Rreset.

Many thanks

Hi Timo,

I think it is the output capacitance and I would suggest evaluating the changes I gave to confirm that hypothesis.

For Rrset 18ohm is on the low side and could result in a large sink current. I would change it to 10kOhm or above.

Hello Marshall,

I have size 1206 10V 47uf on the output side tested .

Currently I have 6 parallel ones, unfortunately still without improvement.

I will now try to test 16V capacitors, I hope that it is still there as you wrote.

Hi,

Marshall is out of office today and will return to provide a response to this tomorrow.

Thanks,
Andrew

Hi Timo,

I was under the impression  that your output voltage was 5V with how your schematic was annotated.

Rereading your initial post, it appears it is 1V. In that case, to compensate the converter even more output capacitance is required than the 5Vout case.

At 6x47uF, I would expect that to be more than enough to stabilize the converter.

Can you confirm that you measure the input voltage and enable voltage measure 12V at the device pin?

Also, can you confirm that the VCC voltage at the VCC cap is ~3V?

Hello Marshall,

I had restocked a board to be on the safe side, unfortunately I didn't have a 16V 47uF currently.
I still use the 10V version.

Here the measured were the output voltage is 1.1V.

Vin=13.5V measured directly on the chip also 13.5V.

GND present on the chip.

VCC measured at input C8 is 3.3V.

At the input and output coil 1.1V each.

But we need 5V at the output.

Thank you for the supporting information and clarification, Timo.

It sounds still like a stability issue as VCC is in regulation so the chip is powered on and doesn't appear to be damaged.

By restocking the board, I assume you mean you are now evaluating on a new board.

That is good information to know that this issue is seen across multiples boards.

6x47uF, 1210 MLCCs should be enough to stabilize the converter.

Do you have the layout for me to review?

I am afraid I am at a loss if your layout looks good.

Hello Marshall,

can i send the altium or eagel file?

Hi Timo,

I can work with the image you provided. Thank you.

While this is probably not root cause, the boot capacitor could be routed better. Please refer to the image on the right with how boot cap is routed.

Can you provide me start up waveforms (Vin, SW, Vout)? And also steady state waveforms with same nets?

You can evaluate at nominal conditions.

Also, can you confirm the loading on the device when it reaches steady state? Maybe the device could be going into current limit.

Many thanks for help,

When I'm back in the company tomorrow I'll try to send the waveform. Currently there is no load on the chip, only an ESP32 XIAO. Later, the chip will supply an LEDarray with SK6812 LED about 5A. Need the chip a Load?

You are welcome, Timo.

Hopefully the waveforms will be helpful in understanding what the issue maybe.

the chip doesn't require a load, I am just trying to make sense why the output may not be in regulation. One reason could be the device is going into overload/short circuit protection. With a 5A load, that shouldn't be the case.

I will consult with some other colleagues with the waveforms you provide to get insights to what maybe occuring.

Hello Marshall,

i hope it will help.

Need you more, please let me know:

Many Thanks!

Thank you, Timo.

I would like to see the startup as well.

Example below

If you could, please measure Vin, Sw, Vout and also PGOOD.

I would like to understand if Vout startups in regulation and then falls.