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Yeah the datasheet state max frequency should be 1.5MHz

Yes clearly it is fake chip. One thing I noticed also when I increase Vin is that the switching frequency is slightly decreased to 1.5Mhz which is  another sign of fake chip.

the attached image shows a genuine chip on a device drawing 50mA VS my PCB drawing 50mA, same Vin and same components value, only the chip is different

Ahmad_k: "I noticed the switching frequency was 1.75Mhz" It's convincing evidence in the direction of suspicion regarding ic. They often just overwrite labels on similar pin compatible  ics or sell pass failed of quality control or bad clones. My experience with digital ics from China is in most times ok, but analog/mixed and similar ic's is not good even I use it significantly below declared characteristics and for simple purposes.

If you have any wishes you can try with <22uH but with open core option (Of curse, Vin will be limited but >12V as now ). That inductors are generaly more suitable for higher freq. Be careful when connecting to keep parasitic capacitance to a minimum.

If not, we expect report for 15 days

I am sure I am using 1A coil. also if the coil was saturated it would heat at least a little. the coil still cool even if the chip heated above 13V

This is me just spitballing. But are you sure the inductor is up to snuff current and frequency way. The datasheet mention that saturating the inductor may cause the device going into thermal shutdown mode and the possibility of damaging the inductor. See the datasheet page 7-8

Check waveform voltage on C8. C8 shouldn't be under 100-150nF (C8 is for supply driving circuit in active cycle so it must not be too low). I thougt add to them parallel 1-10nF (I not expect too much from this but try).

For inductors you used, what is declared current? (I ask beacuse of possible saturation. Bigger inductance for same size mean lower saturation current...).

I suspect on IC, but you check all other (beacuse of very high switshnig freq these ics are sensitive so layout also can cause different problems)...

1A max current coil. So it should be safe. I still suspect the IC as you said because I noticed the switching frequency was 1.75Mhz which is outside the limitation.
I will order from trusted reseller and report back in a week or two

Check waveform voltage on C8. C8 shouldn't be under 100-150nF (C8 is for supply driving circuit in active cycle so it must not be too low). I thougt add to them parallel 1-10nF (I not expect too much from this but try).

For inductors you used, what is declared current? (I ask beacuse of possible saturation. Bigger inductance for same size mean lower saturation current...).

I suspect on IC, but you check all other (beacuse of very high switshnig freq these ics are sensitive so layout also can cause different problems)...

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