LM25149-Q1: Observing Diode Emulation operation instead of FPWM

Prem Ankitkumar Shah

Part Number: LM25149-Q1
Other Parts Discussed in Thread: LM25149,

Hi,

I am using LM25149 for the Sync Buck converter to operate on Continuous conduction mode , I connected the PFM pin to VDDA to ensure FPWM operation as suggested in datasheet; also while converter was running, Checked both PFM and VDDA and found them both on 4.959 V. What might possibly be the reason why the converter is operating in DCM or diode emulation mode?

parameters: Vin:12 V, Vout required : 4.9-5 V, Iout=3A, L=2uH, Cout=220uF, fsw=200kHz.

Results shown above : Yellow :Vout, Blue : IL, Magenta: Vsw

Thanks,

Prem.

over 4 years ago

+1 Timothy Hegarty over 4 years ago

TI__Guru* 75882 points

Hi Prem,

PFM is active high, so tie the PFM pin low for CCM (it's opposite logic to DEMB in previous generation controllers).

Regards,

Tim

+1 Orlando Murray over 4 years ago

TI__Mastermind 22302 points

Prem,

As Tim says tie PFM to GND for FPWM operation.

The LM25149-Q1 Datasheet has been updated, please download the latest revision (with updated PFM description).

-Orlando

0 Prem Ankitkumar Shah over 4 years ago in reply to Orlando Murray

Prodigy 140 points

Hi Tim and Orlando,

Thanks for clearing that up for me. I was hoping that was the only possible explanation, but due to having older version of datasheet, I got stuck.

Thank you,

Prem.

0 Timothy Hegarty over 4 years ago in reply to Prem Ankitkumar Shah

TI__Guru* 75882 points

Thank you, Prem.

Power management

Power management forum

LM25149-Q1: Observing Diode Emulation operation instead of FPWM