LM25116: Current limit doesn't work properly.

user6262012

Part Number: LM25116

Hi.

In the attached circuit, I checked current limit when a single short-circuit failure is occurd.

But the I_out didn't stop and R_s was extremely heated, finaly the high side MOSFET would burn and be broken.

In the same time I watched the voltage at UVLO pin, and it doesn't work as proper t_ss following C_ss.

So I think the IC dosen't do STOP and RESTART sequence properly.

　change time scale⇒　

Tell me the reason why the Current limit does't work.

Thanks for your kind replies everytime :)

0 EricLee over 3 years ago

Hello

I think R202 is affecting the cycle-by-cycle current limit. Would you please retest without it.

- Eric Lee (Applications Engineering)

0 user6262012 over 3 years ago in reply to EricLee

Thank you for replying.

The result above is without R202.

Any part surrounded by a square is not mounted on the board.

Regards.

0 EricLee over 3 years ago in reply to user6262012

Hello

Would you please retest with >=470nF capacitor at C120 ?

-Eric Lee (Applications Engineering)

0 user6262012 over 3 years ago in reply to EricLee

Hello

I mounted 100nF at C120 ( 470nF is outof stock ;d ), then I got the wave below.

I understood that to prevent short-circuit power dissipation , It is necessary to determine t_off with C_ft.

t_off would be calcureted as about 700 us but V_UVLO below doesn't behave like that.

This waveform is OK?

+1 EricLee over 3 years ago in reply to user6262012

Hello

Yes, the waveform looks good now.

t_off is measured from the time UVLO starts falling to the time UVLO crosses over 1.215V.

-Eric Lee (Applications Engineering)

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