CSD19536KTT: Using CSD19536KTT in a linear regulator application

Hello Frank,

Thanks for your interest in TI FETs. The CSD19536KTT is TI's lowest on resistance 100V FET. Although, resistance is not as critical for a linear application where the FET is operating in the saturation region. What are your current requirements and maximum case temperature for the linear regulator? The SOA graph in the datasheet is taken at a case temperature of 25°C and should be derated for elevated operating temperature as explained in the technical article at the link below. The second link is to a blog explaining how TI tests and specs SOA for our FETs.

https://www.ti.com/lit/an/sluaao2/sluaao2.pdf

http://e2e.ti.com/blogs_/b/powerhouse/archive/2015/05/02/understanding-mosfet-data-sheets-part-2-safe-operating-area-soa-graph

Best Regards,

John Wallace

TI FET Applications

Hello John,

Thanks for the reply.  The application is for a pulsed load application: 16 Apk at 30% duty factor.  The goal case temp is 100C. Thanks for the links to SOA vs temp.

The reason for the question regards the type of FET.  The CSD19536 is not a "trenchFET" but the comment was made it is still a FET optimized for switching applications rendering it suboptimal for a "DC" linear regulator application.  That is my concern.

Cheers,

Frank

Hi Frank,

Apologies for the delayed response as I was off for the holidays. Although the CSD19536KTT is optimized for switching applications, it can still be used for a pass element in a linear regulator application. For your application, you need to use the normalized transient thermal impedance graph in Figure 1 of the datasheet to estimate the junction temperature at your operating conditions. Please see the links below for more information on how to use this graph. Also, please note that you may be able to use a lower cost FET if it still meets SOA and the estimated TJ < TJmax. Let me know if you need help with the calculations.

https://www.ti.com/lit/pdf/SLUAAO2

http://e2e.ti.com/blogs_/b/powerhouse/archive/2015/06/29/understanding-mosfet-data-sheets-part-4-mosfet-switching-times

Thanks,

John

Hey John,

Thanks for the response.  I had looked at the SOA for the CSD18/19536KTT devices for the application. It seems like a good candidate. 

Unfortunately, the application we're looking at involves another company who has chosen a different device based on the device's data sheet which specifically "for linear applications."  That device's SOA is inferior to the CSD19536KTT.  The other company's claim is that the CSD19536KTT has a structure that would lead to localized hot-spots in a linear application whereas the device they've chosen has a different FET structure.

That is the reason for my prior texts.  I am just trying to ensure that there is nothing to the other company's argument.

Thanks

Frank