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CSD19505KCS: paralleling MOSFETs

Howard Zou
Genius 12365 points
Part Number: CSD19505KCS

Hi,

my customer has been using CSD19505KCS for long and now they find some devices break down during the test. They suspect that using different LTC CSD19505 in parallel may be the cause of the break down, since the parameter mismatch may cause some MOSFETs to turn on before others, which exceeds the maximum rating of the device.

I would like to know:

1. Is it true that we should not use different LTC CSD19505KCS in parallel?

2. What considerations need to be taken when connecting MOSFETs in parallel?

3. If we connect 5 MOSFETs in parallel, and the peak current needed is 100A, what current rating MOSFETs do we need?

  • 0
    TI__Mastermind 29535 points

    Hi Howard,

    Thanks for promoting TI FETs at your customer. What is the application? Is the FET being used in a switch mode power application such as power supply or motor drive? Or, is it a static switch application such as hot swap, OR'ing or battery FET? In general, MOSFETs parallel well with some precautions. You are correct that parameter mismatch, threshold voltage, can result in one FET turning on first and turning off last and take more the stress during switching. There also will be lot-to-lot variation of threshold voltage. To answer your questions:

    1. No, you still should be able to parallel FETs from different lots.
    2. Each FET needs to have it's own gate resistor (a few ohms up to 10 ohms). Placement and layout of FETs should be made as symmetric as possible with gate trace length the same for all FETs. Try to keep the FETs as close thermally as possible by using a common heatsink.
    3. Datasheet current ratings can be confusing. Please check out the blog in the link below. The number of parallel FETs depends more on power dissipation than current ratings of the FETs. Is 100A the static current?

    I am going to close out this thread and contact you via email.