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I am working on making a board for the Hummingboard System on Module using the company's board schematic as a guide. They use a TSM2323 mosfet in the "micro SD power on/off" section of their schematic (page 2). As this component is hard to come by I am looking for a replacement MOSFET, but I am not confident in my ability to find a suitable replacement. I would appreciate any suggestions, preferably from Digikey's products.

I found some information online for how to find a replacement MOSFET, but with the sheer number of different MOSFETs to choose from within Digikey's catalog, I am not confident in the replacements I find on my own.

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2 Answers 2

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When searching for replacement, you should look at the first few words of the transistor datasheet. In this situation your keyword is ultra low on resistance. I seached for digikey with similar r ds on resistance. I found that Si3433CDV has very similar characteristics with your transistor. In general, if Vds and Vgs graphs at the datasheet are similar you can use that MOSFET for replacement.

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  • \$\begingroup\$ That does seem similar to what I need and I appreciate the info, but could you tell me two things: 1. What were the exact filters you used to find this on digikey? 2. How do you know if the Vds and Vgs graphs are "similar?" I haven't used mosfets and I would like to learn exactly how you found it so I don't have ask again for the next mosfet for which I need to find a replacement. If I am asking too much, just tell me where to shove it :P. \$\endgroup\$
    – Nate
    Dec 16, 2014 at 0:19
  • \$\begingroup\$ I searched 'mosfet' word in digikey search area. Then I clicked FETs - Single (35770 items). In FET type area I select MOSFET p-channel, metal oxide. Then the only parameter I looked for is Rds on resistance in 'Rds On (Max) @ Id, Vgs' area. I selected near values of 39mili ohm, 4.5V, 4.7A. like 38mili ohm 4.5A 5V. After selecting bunch of near values, click apply filters. An importing thing for selecting component is, it should be available in immediate stocks. \$\endgroup\$
    – electro103
    Dec 16, 2014 at 5:25
  • \$\begingroup\$ You are awesome, could you tell me how to tell if two Vds and Vgs graphs are similar? The drain current levels off at somewhat different amounts in the Vds graph and the drain current reaches the same point at a slightly different voltage in the Vgs graph. Aside from that they have a similar look. Could you provide an example of a mosfet where the graphs aren't considered "similar enough" for contrast so I can tell the difference between graphs that are similar and those that are not? (This should be my last request.) \$\endgroup\$
    – Nate
    Dec 16, 2014 at 7:03
  • \$\begingroup\$ Actually, selecting replacement component, one should know the which properties of the component are used in a particular application. I do not have an idea why the designer use pwm for powering sd card. Knowing why helps to identify which mosfet features are most important for selection. For your application, vg voltage is digital either high(5v or 3.2v) or low (0v). So you should look at vgs=(3.2v or 0v),vds=(3.2v or 0v). Also timing is an important issue. If your pwm freq>5 GHz there will be problems in si3334. For your question look at different p channel fets, you will see the difference. \$\endgroup\$
    – electro103
    Dec 17, 2014 at 4:25
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I haven't looked at your circuit and neither do I intend to but here are some guidelines: -

You have to decide on several things and all of those things you clearly don't know about or you would probably have put them in the question: -

  • Maximum voltage rating and what the circuit might generate
  • Maximum current rating (average and instantaneous peak ratings)
  • On resistance - does you circuit require to turn on a heavy duty load with minimal volt drop?
  • Gate-source threshold voltage - your circuit might be fine with the old mosfet but picking one that might be tailored for best performance may be a little long-winded.
  • Switching speed may or may not be that important in some applications.
  • Gate-source capacitance - may need to be especially low
  • Drain-source capacitance - ditto above.
  • Package type.

Good luck and learning.

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