LMR14020: The output should be 4.22V but the real test result is 4.38V.

Hi Amelie,

There could be some drop in your output trace. Where are you measuring the output voltage? Is it at the point where R407 connects to the output?

Can you share the layout of this power section? 

Thanks, Jason

Hi Arrigo,

Thanks for your reply. I understood there could be some drop. But the questions is calculate value is 4.22V, even less than the test result...

I will ask customer to provide the PCB layout later.

Hi Amelie,

Sorry, I misread your original post. 

Since the measured voltage is higher than the calculated, you need to consider the tolerance of the FB voltage and the FB resistors. However, the difference is still a bit high based on tolerances. Please check the R values just to be sure the correct values are populated. Does this offset show up on multiple boards or just one board?

Also, when they are measuring the voltage, where is their ground referenced? Are the FB resistors located close to the device FB pins and GND pins? 

Regards, Jason

Hi Jason,

• The tolerance is 1%;
• Customer test the R406 point voltage.
• I also review customer layout  and found RFB is also very closed to the chip.

One more test result from customer is

• When change from 118k/25.5k to 10k/2.2k to get 4.22V, the test result is 4.35V(118k/25.5k) and  4.22V(10k/2.2k ).

It seems when choosing small value of res, the voltage could be more stable.

• When change the Vin from 12V to 24V, the Vout also have a big gap, Vout=4.19V(Vin=12V);Vout=4.27V(Vin=24V)

May I ask the accurate of Vout？ 1%? How could customer maintain stable 4.22V output?