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For C8 I didn't try any value below 100nF as the datasheet recommended a Cap of 150nF.
For the inductor I tried 22uH, 47uH, 68uH, 220uH. Higher the inductor value, higher falling time.

I will check the waveform on C8 tomorrow

Clone IC's can be problem in most cases (they usualy sell it as LMR14203 but real chip work only for low voltages - many users will use it for 12 to xx converters so no problems

@between SW and GND -> im not sure but...that possible means that conveter work in dcm mode. It can produce problem for bootstrap voltage because C8 can't charge and it produce many other problems for this type of converter (did you try for C8: 10nF + 0.1uF-1uF?).

1. Check with scope voltage on C8.

2. What inductor you use? Did you try with inductor for much bigger current (22-47uH, 1A or etc...)?

I think for fixed voltage output you need to recalculate the swicthing ferquency CAP (CB ) and L1 or use values that used in demonstration board user guide.

https://www.ti.com/lit/ug/snva502b/snva502b.pdf?ts=1744980548862&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLMR14203

sadman

I did follow the datasheet and the application note, those values in the schematic are just for reference, I did try a lot of different pairs or Cboost and Inductor

1) Under what conditions (Vin, Vout, Iout...) is waveform?

2) waveform you show is voltage at U5.6 - GND  or U5.5 - U5.6?

3) Is your IC's genuine (many asian clones can be problematic)?


@sadman about swicthing ferquency CAP (CB ) - I think CB(8?) isn't swicthing ferquency CAP, it's bootstrap cap for driving internal mosfet?

Vin was 10v, Vout 5.1V I=50mA Only.

Now I start believing that maybe it could be a clone. I spent all the day trying different values. I will order another batch from different seller. Those chips I have now can be used for input below 13v without any issue.

First I thought that my ceramic capacitor was 16v only and I said that's it, but it was 50v

Posted on: April 18, 2025, 06:24:19 18:24 - Automerged

2) waveform you show is voltage at U5.6 - GND  or U5.5 - U5.6?
@sadman about swicthing ferquency CAP (CB ) - I think CB(8?) isn't swicthing ferquency CAP, it's bootstrap cap for driving internal mosfet?

between SW and GND

1) Under what conditions (Vin, Vout, Iout...) is waveform?

2) waveform you show is voltage at U5.6 - GND  or U5.5 - U5.6?

3) Is your IC's genuine (many asian clones can be problematic)?


@sadman about swicthing ferquency CAP (CB ) - I think CB(8?) isn't swicthing ferquency CAP, it's bootstrap cap for driving internal mosfet?

I am developing a tiny device that can handle DC input from 8 to 30V 100mA max, so my choice went to LMR14203 as I see it a lot of devices and it is working great.
I replicated the same PCB mentioned in their application note but I have weird result. The falling time of switching signal is high.
That's not a problem when my input is below 13V. Increasing it will make my signal near SAW TOOTH format and the chip starts heating even on 50mA load. Does anyone know what factor am I missing ? can be saturated coil or what ?
The falling
 time on a working LMR14203 is so small compared to my result

I think for fixed voltage output you need to recalculate the swicthing ferquency CAP (CB ) and L1 or use values that used in demonstration board user guide.

https://www.ti.com/lit/ug/snva502b/snva502b.pdf?ts=1744980548862&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLMR14203

sadman

I am developing a tiny device that can handle DC input from 8 to 30V 100mA max, so my choice went to LMR14203 as I see it a lot of devices and it is working great.
I replicated the same PCB mentioned in their application note but I have weird result. The falling time of switching signal is high.
That's not a problem when my input is below 13V. Increasing it will make my signal near SAW TOOTH format and the chip starts heating even on 50mA load. Does anyone know what factor am I missing ? can be saturated coil or what ?
The falling time on a working LMR14203 is so small compared to my result

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