L6982C33DR & L6982C50DR always provide 2.5V output

[Sheng123]

Dear Community,

I’m currently testing the L6982C33DR and L6982C50DR to supply 3.3V and 5V to my board.

I followed the reference design provided in the user manual and completed the PCB layout accordingly.

However, when I power the board with 12V (Power+), both the 3.3V and 5V outputs are only showing 2.5V.

I’ve attached my design files for reference. Could anyone help me identify what might be going wrong?

Thanks in advance for your support!

 

[Peter BENSCH · Accepted solution]

If you have measured as shown in the schematics, i.e. without any load and with these values of R1...R4, it is no wonder that you cannot achieve a meaningful result. Please replace each of the R1...R4 with a bridge and connect a real resistive load to each of the outputs, e.g. 12...20 ohms or less.

Hope that helps?

Regards
/Peter

[Sheng123]

Dear Peter 

Thanks for answering, we have removed and shorted the R1~4 and the Value has become normal
However the R_FBH & R_FBL on the user manual is quite misleading, it also shows on the Schematic,

[Peter BENSCH]

The data sheet for version 1 only contained the adjustable version, later the fixed version was added. The colleague responsible had removed the feedback resistors from the drawing, but unfortunately not their labelling, for which I would like to apologise. This will be corrected in the next revision.