LM3488: LM3488 isn't working correctly

Schematic :

Curve 1 (board KO : COMP signal + switching transistor)

Curve 2 (board OK : Vout + COMP)

Curve 3 (board KO : Vout + COMP)

Hi Romain,

Thank you for your interest in LM3488.

Could you please let me know the output current and confirm the input/output voltage for me?

Thanks,

Yinsong

Hi Yinsong,

Output current : 1A (max).

Input voltage : 8V to 18V

Hi Romain,

Thank you. It looks like the cycle by cycle current limit from the rough calculation. Do you have the ISEN waveform?

Thanks,

Yinsong

Hi Yinsong,

ISEN waveform looks good (no short-circuit level detection). 

Isen (pink waveform)

Isen (green waveform) / Comp (pink waveform)

I removed a 0.07 ohm resistor to increase Rsense and I had no improvement.

I changed also compensation with R132 = 3.3Kohm and C70 = 100nF with no improvement.

I changed R127 (220K to 100K) to increase swiching frequency to be in component specifications with no improvement.

Thanks for your help,

Romain

Hi Romain,

Thank you for the trials and information.

One thing that bothers me is that the Isen looks half positive and half negative. Have you checked the zoom in waveform of it with one switching cycle?

If possible, please show the time range in several cycles Isen with the SW voltage. Also, please check if it is repetitive when you capture it.

Thanks,

Yinsong