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PMP20183: PMP20183 High current draw issues

Part Number: PMP20183
Other Parts Discussed in Thread: LM3481, CSD19538Q3A, CSD17577Q3A

Hello, I have implemented PMP20183 for the most part copying the schematic and layout except for modifying the R2,R100 and R3 according to post "PMP20183: PMP20183 Voltage modification" on these forums to 6.34k, to lower the overall output voltage. However, I am reaching an issue hitting the target voltage, from what appears to be excessive current draw. Essentially, the LM3481 drives the FET for  a few ms, the 12V power supply voltage goes down, eventually triggering the UVLO. It then takes some time to recover. The overall output voltage is around 100V, well below the expected. The thing is the overall circuit is only drawing ~150mA, so it's not overloading my power supply, so I figured it might just need more capacitors (not listed on the design) for burst current, however adding a a few more 22uFcaps, and then a 1000uF cap to the supply and near the inductor seems to make the driver run for longer, but then the overall current becomes something like 0.5A, the final output voltage only reaching something like 110V. I also tried increasing the input voltage, and at ~12.5V the current spikes up again and blows the mosfet. Kind of tearing my hair out about this, so any help would be great!

I attached some waveform, yellow is output voltage, blue is the drive signal. Isense voltage seems below 200mV.

  • Charles,

    It is difficult for me to be able to trouble shoot the circuit to find the issue. A few thoughts for you to consider:

    - Are any components installed incorrectly, such as a diode installed backward. Very carefully check all components on the board.

    - Are the components you are using the same as what is on the PMP20183 bill of material. Are any of the parts different (FET, diodes, inductor, ceramic caps)?

    - Is there a load on the output or is it unloaded? If so, what does it do when unloaded?

    - Also verify your load is resistive (a resistor) and not an active load. It is only a 2W output and should not be pulling the input source down.

    - Are there any additional output caps on the output other than what PMP20183 shows?

    - Is the inductor saturating? I believe the peak current should be ~1A.

    - Verify the FET you are using has fast switching capabilities and can be fully enhanced at 6V (or lower if Vin <6V). Make sure the FET is rated at 4.5V Vgs.


    John Betten

  • I doublechecked the  diodes, and they appear to all be in the correct direction, and all seem read proper voltages with my multimeter.

  • Don't know why TI site removed the rest of my response. I also said that it is under no load conditions, with no other capacitors. I tested it with a resistor, but the output voltage dropped. but as per your note, I double checked I was using all of the exact parts for the design, and noted that I was using a CSD17577Q3A instead of a CSD19538Q3A. Ah I must of just selected a part that looked very similar on digikey! But I think that the different fet characteristics, like you mentioned as your last comment could be causing the issue. Going to order that fet and see if that fixes my problem.

  • Charles,

    The CSD17577Q3A FET is rated at 30V, which is very likely the issue.

    In the PMP20183 circuit, the FET will see Vout/3 = 200V/3 = 66V, since it has a voltage tripler. If your application is 180V, the FET will see about 60V. It is very likely the FET you are using is breaking down slightly above its 30V rating. You will require a higher voltage (100V) FET for 180V output. A 60V FET is not recommended because it would not have a standard derating of 80%. A FET with a 75V to 100V rating is acceptable for a 180V output.


    John Betten