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WEBENCH® Tools/CSD18543Q3A: Looking for CSD18543Q3A parts or alternative part of the same footprint

Part Number: CSD18543Q3A
Other Parts Discussed in Thread: CSD17308Q3, LM25141, CSD19537Q3, CSD17575Q3, CSD17304Q3, CSD17309Q3, CSD16327Q3, CSD16340Q3, CSD16323Q3, CSD16411Q3

Tool/software: WEBENCH® Design Tools

Hi,

I designed 24VDC to 6V DC/ 2A converter circuit with the help of WEBENCH and already got the PCB. Now it is time to assemble the boards for evaluation, but the low side MOSFET, CSD18543Q3A, is out of stock in any distributors. Is there any way to get the parts? For now, I need only three.

Texas Instruments, could you recommend the alternative part of the same footprint (VSON 8, 18mm2)?

CSD17308Q3 is used for high side MOSFET. I am  also wondering if I can use this for  CSD18543Q3A.

For your information, here is the WEBENCH ID: 

1104891/89 LM25141RGER

I will appreciate any help or advice.

Thank you.

Best regards,

Dennis

  • Dennis,
    We may be able to help you out in this special circumstance, although I am a bit surprised the design recommended you use a 30V FET for the HS and a 60V FET for the low side. There may be a more optimized solution.

    In addition to webench, I would recommend playing around with our online buck converter tool to see if you get recommended the same FETs.

    webench.ti.com/.../FETPBWizard.jsp

    I am going to friend request you so we can take a conversation about samples offline.
  • Hi Brett,
    Thank you for your follow-up.

    So I tried your recommended tool, "MOSFET Power Loss Calculator", with LM25141 controller and CSD17308Q3 for HS FET fixed.
    I set the other parameters as followings: Vin = 24.0V, Vout = 6.0V, Iout = 2.0A, L1 = 5.0uH. F_pwm = 2MHz.

    I played with LS FETs of SON3x3 package, but the total Pd was more than 1.4W.
    At the WEBENCH design of CSSD18543Q3A, I got only 0.76W.

    I saw CSD19537Q3 (Vds max = 100, I max 50A) available. I am wondering if I can use this part instead.
    For now, I cannot see this part at both " WEBENCH "and "MOSFET Power Loss Calculator" tools.

    Best regards,

    Dennis
  • Dennis,
    I will look into the power loss discrepancy for you. Can you confirm the Pd you are referring to was of the LS FET specifically, and not the total power loss?

    The MOSFET Power Loss Calculator does tend to take into account second order effects like common source inductance that are particularly detrimental at higher frequencies (2MHz is really pushing it for this input voltage) and also assumes a higher junction temperature, so I am more inclined to believe those numbers but I will investigate.

    You could in theory use the CSD19537Q3 but the CSD18543Q3A is lower gate charge, lower resistance, and less expensive. The CSD18543Q3A is certainly a better solution than the CSD19537Q3, and it will actually be easier to get you samples of the CSD18543Q3A.
  • Hi Brett,

    Attached is the WEBENCH design report.

    You can access the following shared link of a clone project, too:

    https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=DD5AABD6F55F7C64

    Unless I can get the samples of CSD18543Q3A in a week, I need to find an operational alternative. Since the PCB is already made, I have to use  SON 3.3 x 3.3 mm (DNH0008A) type only.

    (cf. I have CSD17308Q3T parts for high side FET )

    The following parts are available at Digi-Key.

    CSD19537Q3
    CSD17575Q3
    CSD17304Q3
    CSD17309Q3
    CSD16327Q3
    CSD16340Q3
    CSD16323Q3
    CSD16411Q3

    Can you tell me which one is most appropriate among these, please?

    I am also wondering if I can use  CSD17308Q3T for both HS and LS.

    Thank you for your time and help!

    Dennis

    webench_design_1104891_89_120388166.pdf

  • Dennis,
    Ok, webench is pretty conservative when it comes to ringing on the LS FET it turns out, which is why you are being recommended a 60V FET.

    If you are based in the United States, accept my friend request and I can send you 3 parts directly. Otherwise, I would recommend the CSD19537Q3.
  • Hi Brett,
    That's great! It's very nice and kind of you.

    I already accepted your friend request.

    Our office is in San Ramon, California, If you don't know our address, please email me. I will let you know

    dkong@rheosense.com

    Thank you so much.
    Best regards,

    Dennis