Part Number: TPS65131
I have a problem with TPS65131. It can not regulate under load.
Designed output voltage: +5V -5V
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
2) Input voltage: 3.3V 270mA load on both outputs
-5v output: 0v
+5v output: fluctuating between 3.6v and 3.85v
3) Input voltage: 5v No load
-5v output: -5v stable
+5v output: +5v stable
4) Input voltage: 5v 270mA load on both outputs
+5v output: 4.7v (sometimes it goes down to 3v)
Board layout: https://i.hizliresim.com/kM8Y9W.png
Any help would be appreciated
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
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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.
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.
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.
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