TPS65131-Q1: Output voltage unstability

Prodigy 100 points

Replies: 14

Views: 253

Part Number: TPS65131

I have a problem with TPS65131. It can not regulate under load.

Designed output voltage: +5V -5V

Symptoms:

1) Input voltage: 3.3V    No load    

-5v output: fluctuating between -2v and -12v (If I add large electrolytic cap to C28, -5v stable with no load, but with 50mA load it goes down to 0v)

+5v output: 5v stable

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2) Input voltage: 3.3V    270mA load on both outputs

-5v output: 0v

+5v output: fluctuating between 3.6v and 3.85v

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3) Input voltage: 5v    No load

-5v output: -5v stable

+5v output: +5v stable

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4) Input voltage: 5v    270mA load on both outputs

-5v output: 0v

+5v output: 4.7v (sometimes it goes down to 3v)

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Schematic: https://i.hizliresim.com/p5NYb0.png

Board layout: https://i.hizliresim.com/kM8Y9W.png

Coil: vls3015cx-4r7m

Any help would be appreciated

14 Replies

  • In reply to Liaqat Khan:

    I tried different things. While the PCB is hot +5v output is stable with 270mA load. So i tried masking the pcb and heating the components one by one. I found that heating R27 and R30 with hot air gun fixes my +5v issue. But i cant figure it out why this is happening. It cant be assembly issue, it is happening all of my 3 boards. I tried changing this resistors but no affect. 

    R30: Yageo RC0603FR-07180KL

    R27: Yageo RC0603FR-07562KL

  • In reply to Mert Aysoy:

    Since these resistors  form feedback divider, it suggests some possible sensitivity to noise on FBP/FBN. Can you please try below two suggestions separately:

    -    reduce resistors R30 and R24 to 130K and recalculate R27 and R25 accordingly to achieve desired VPOS/VNEG voltage to see if this improves the behavior?The reason is: making more current flow through lower feedback resistor should reduce FB pin noise.

    -  make series resistors with C12 and C26, that I suggested earlier,to around 100K.

    Kind Regards,

    Liaqat

  • In reply to Liaqat Khan:

    I changed R30 and R24 to 120K (i dont have 130K in stock) and calculated R27 and R25 accordingly, but this dont solve my issue.

    I changed series resistors with C12 and C26 to 100K and but no change. Same issue. 

  • In reply to Mert Aysoy:

    Hello Mert,

    At this point, without actually having the board with me to test in the lab, it may be hard to figure out the cause of this issue. Unfortunately, I don't have any further suggestions.

    Kind Regards,

    Liaqat