LM5119: Low-side PWM operation problem in DCM mode

Seung-Ug Baek

Part Number: LM5119

Hello

We are looking for a solution to the problem that Low Side FET does not switch when operating with DCM. The output is normal, but the heat of the LOW side FET is a problem.

R and C of RAMP checked the datasheet and tried to change it, but it was not resolved.
(I tried setting RAMP C lower than 2nF.)

over 2 years ago

0 Mahmoud Harmouch over 2 years ago

TI__Mastermind 26160 points

Hello,

I checked the waveform and looks normal in DCM mode. Is the lower power FET heat noticed only DCM mode? Is the lower power FET temperature looks OK in CCM mode?

The lower power FET body diode is conducting the inductor current during OFF time. The FET body diode usually has higher voltage drop than the channel Rds/on.

Please check the FET body diode forward voltage VF. You can calculate the lower FET power dissipation in both mode DCM and CCM. This tells you the power dissipation difference and the temperature rise may due to that.

Regards

0 Mahmoud Harmouch over 2 years ago in reply to Mahmoud Harmouch

TI__Mastermind 26160 points

Hello,

I did not receive an answer so I consider the issue is resolved and I'm closing the thread. Please let me know for further support

Regards

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LM5119: Low-side PWM operation problem in DCM mode