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PTH03030W output voltage drop

yonggang ma
Prodigy 30 points
Other Parts Discussed in Thread: PTH03030W

I use PTH03030W to generate 1.8V from 3.3V for 24 DDR2 memories and their controllers(4 FPGAs). When power-up, it is OK for them and output is 1.79V(current 1A). But after I load one FPGA , it drops to 1V around. I donot know why. So, anyone can help me? Thanks!

  • 0
    Genius 4530 points

    Hi,

    Which FPGA are you using? Depedning on the device, have you done current calculations for the same? Virtex devices tend to have much larger current requirements depending on the loads you are driving. Its obvious that the source is getting loaded, which maybe due to inappropriate current calculation or some short circuit on board. have you checked the board for short circuits?

    Regards,

    Sid

  • 0 in reply to Sid
    Prodigy 30 points

    Hi,

    I am using Virtex5 SX95T. I have done the power estimation via the power estimation tools from Xilinx. The norminal max output current of PTH03030W is near 30A(1.8V output), which is much higher than my condition, cause I only load one SX95T.  I donot find any short circuits and it works fine until I load the FPGA with program related with 1.8V. I plan to check whether it is over-current tomorrow. Anyway thanks for your suggestions!

    Regards,

    Yonggang

  • 0 in reply to yonggang ma
    TI__Mastermind 38230 points

    Hi:

     

    Can you send the schematic of this application ?

    I suspect the DDR portion is loading down the module. How is the remote sense function attached to the output bus? It must be connected directly to the output power pins of the PTH 03030W . It cannot  be connected  isolated  by any impedance / resistance.on the load side .

    How is the Rset pin  connected to ground  or controlled?

    Tom

  • 0 in reply to Tom Guerin
    Prodigy 30 points

    Hi,

    It has solved on the other day. The root cause is the power cable from the board to DC power, which is not good. It has a large voltage drop, when 24 DDR2 run together. Nominally, the 3,3V rail has 10A current at that case. So, the input 3.3V drop lead to the 1.8V power module working unnormally and the output also dropped. After we change the cable, it works fine.

    Anyway, thank you for your suggestions!

     

    Yonggang