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CSD18510Q5B: Undrestanding the SOA

toktam khani
Prodigy 140 points
Part Number: CSD18510Q5B
Other Parts Discussed in Thread: LM74910H-Q1

Hi,

it seems that i do have  aproblem with undrestanding of the SOA. i am looking for MOSFET for my ORing IC (LM74910H-Q1). 

assumptions: 6A, Vmax=34V, VGS=10V, @100°C: RDS-ON = 1.45*0.79mOhm=1.1mOhm

my selection process is: 

1- VDS = 6A*RDS-on = 6A*1.1mOhm = 6.6mV

2- look at figure 10 of the datasheet. extending the RDS-ON limit line (gray) to VDS=7mV -> it can handle about 4A continuous at 7mV drain-source voltage. 

image.png

is my method wrong? considering the 1.1mOhm, the power losses of the MOSFET is about 40mW (1.1mOhm*6A^2) which is not a problem. Do i consider wrong VDS for my calculations/selection?

 

BR Toktam

  • +1
    TI__Mastermind 39210 points

    Hello Toktam,

    Thanks for your interest in TI FETs. SOA is mainly a concern when the FET is operating in linear mode where there is voltage across the device while there is current flowing thru it. In an OR'ing application, this normally occurs at turn-on and turn-off. SOA is less of a concern when the FET is turned on and Rds(on) is very low. In this case, power dissipation is the primary concern. You want to take a look at the turn-on and turn-off times of the OR'ing controller to make sure they are within SOA of the FET. I am including two links below. The first explains how TI tests and specs SOA and the second provide guidance on using SOA graph in your design. Let me know if you have any questions.

    https://www.ti.com/lit/pdf/SSZTCR5

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

    Best Regards,

    John Wallace

    TI FET Applications