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PMP22504: ideal bridge diode replace the NMOSFET

Jim Tseng
Intellectual 2320 points
Part Number: PMP22504
Other Parts Discussed in Thread: CSD18541F5, CSD88539ND, LM74610-Q1

HI Expert,

about the ideal bridge diode, could you help to check if we can replace the NMOSFET – CSD88539 by CSD18541*2 to save some board space? Thanks.

Jim

  • 0
    TI__Mastermind 39510 points

    Hi Jim,

    Thanks for your interest in TI FETs. The CSD88539ND is a dual 60V NFET in SO8 package. The CSD18541F5 is a single NFET in F5 FemtoFET package with about double the on resistance per FET. You may be able to parallel 2 of these to get approximately the same on resistance of one channel of the CSD88539ND. However, the CSD18541F5 is not designed for high speed switching and has an internal series gate resistance of 1.2kOhm typical. Because of this, the FET will switch much slower and you may not get the same performance as the CSD88539ND. Also, each FemtoFET can dissipate approximately 0.5W maximum due to the small size.

    Please review this technical article on how much power can be dissipated in TI FET packages. I am going to forward this thread to the LM74610-Q1 apps team to get their input.

    Thanks,

    John

  • 0 in reply to John Wallace1
    TI__Guru 57737 points

    Hi John,

    Thanks for looping Ideal Diode controller in supporting query on LM74610-Q1. Let me look into this and provide my inputs by tomorrow. 

  • +1 in reply to Praveen GD
    TI__Guru 57737 points

    Hi Jim,

    John has covered all the points which are key to consider while changing the Mosfet.

    The LM74610-Q1 has no ground reference and therefore it makes use of the forward voltage drop (Vf ) across the body diode of the MOSFET is used to charge up the charge pump capacitor Vcap. For this reason, the Mosfet is turned OFF and then ON continuously to charge up the charge pump capacitor as shown below. When the FET is OFF the body diode conducts and hence there is power dissipation in the FET .   Since the body diode conduction time is small, the power dissipation is generally not significant. 

    With slower switching of the FET due to its increased gate resistance the power dissipation in the body diode may become significant now. 

     

    You can use the equations provided in the datasheet to estimate  the power loss in the FET (due to Body diode and FET Rdson) for your application and then take call on changing the FET accordingly.