TPS65131: Apply TPS65131 for a dual output power module, +5V input, but -15V output wrong

Hello,

I do not see an attachment in your post. Please attach schematics of your design for review.

Kind Regards,

Liaqat

Hello,

The schematic is same as the datsheet, absolutely same. 

Power Module B(3).rarPower Module B(2).rar

Hello,

I am not able to open the files you attached but if the schematics is same as what is in the datasheet, the only modification I could suggest is to try and add a resistor in series with feed forward capacitor, as shown in the image below, to cut down on any possible noise coupling into FBN pin. Since your design is compact, there may be some noise coupling in FBN and this suggestion would be helpful in cutting down that noise.

Kind Regards,

Liaqat

Disappointed,  I use the 1st version PCB, I add a 49.9k R in series , when I drive a 300R load, the negative became  -0.5v.

Hello,

Can you please attach a screen capture of you schematics and layout or a .pdf of the schematics and layout? I will review it to see if I can spot something that can cause the issue you are seeing. I was not able to open earlier files that you attached.

Kind Regards,

Liaqat

Dear ,

Thanks a lot for your kindly support.

Please refer to the attached material .

Or you can mail to me directly.

Thanks！TPS65131 LAYOUT.pdf

Hello,

I reviewed your schematic and layout. It appears that (at least in the first version of the layout) the exposed center pad of the TPS65131 device is not  connected to the ground. This exposed pad should be connected to the GND. It is possible that I am not able to see this connection due to some layout tool issue like copper pour not shown. If center pad is connected to the GND, I don't see anything else obviously wrong with the design that should cause the wrong output on the inverting converter. The only other explanation is perhaps some board assembly issue where the device is not soldered properly. Unfortunately, I don't have any other suggestions.

Kind Regards,

Liaqat

Dear，

Appreciated for your checking.

The center pad is connected to GND throught via , as you can check the file as attachment .

The refernece layout of TPS65131 is big size PCB , but my PCB size is so small with 2mm X 1mm, I wonder if TPS65131 is not suitable for such small PCB because of interference, need we improve my layout ?

Bestt reagrds！

ZOUTPS65131 LAYOUT V2.pdf

Hello again,

Small PCB size should not be an issue. The problem could possibly be related to a board assembly issue. You could have the board assembly x-rayed to see if the underside of the device exposed pad is soldered properly and also double check the rest of the component values on the assembly. You can check the input supply, VNEG output and SW node waveforms with a scope at no load when the outputs are correct and also at the moment when you apply the load. These scope plots may provide some clues.  I am not sure what else to suggest.

Kind Regards,

Liaqat