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CSD17570Q5B: "Not intended for switching applications"

Part Number: CSD17570Q5B
Other Parts Discussed in Thread: CSD17573Q5B


What are the specific reasons/parameters why TI publishes "not intended for switching applications" for the low Rds N-FET 'CSD17570Q5B'?




  • Hello Tom,

    Thanks for your interest in TI FETs. The CSD17570Q5B was developed for what I would call static switching applications (i.e. turn it on and leave it on) such as hot swap and OR'ing circuits. For this type of application, the key parameter is low on resistance to minimize conduction loss when the FET is on. Charge and capacitance are not as critical as the device is switched on or off relatively infrequently. For switch mode power applications such as synchronous buck converter or as an SR FET, charge becomes a more important factor as it contributes to switching loss and gate drive loss. There is also a phenomenon known as CdV/dt induced turn on where the VDS changes very rapidly which can result in an increase of VGS turning the FET on when it is supposed to be off. To minimize this effect, the charge ratio Qgd/Qgs is optimized to be < 1. For the CSD17570Q5B, this ratio is 34nC/27nC > 1 which means this device is susceptible to CdV/dt induced turn on when it is used as the sync FET in a buck converter or SR FET in other DC-DC converters. This can lead to shoot thru or cross conduction where both FETs are on at the same time increasing the power loss. We do not recommend this FET for switch mode applications as the performance will not be very good. Our lowest on resistance 30V FET in 5x6mm SON package is the CSD17573Q5B which has a charge ratio of 11.9nC/17.1nC < 1.

    Best Regards,

    John Wallace

    TI FET Applications