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LM5060: Reverse Polarity Protection With Diodes

zaf sen
Prodigy 20 points
Part Number: LM5060
Other Parts Discussed in Thread: TPS4811-Q1, LM74502,

Q1. Can you please share with me the details of D1, D4, D5, D6 and D7 diodes for example design 2 on page 27 in the datasheet? (the part number would be great)

Q2. This question seems it is a general question about MOSFETs but What is the important thing we are picking up a mosfet for the example design: LM5060EVAL Design. For example, my system requirements are like these:

Operating voltage range 14V to 24 V, Current max 13A , OVP setting 27 V typical UVLO setting 12 V typical.

So in that case, I try to keep Rdson res lowest value as much as possible when I am choosing a mosfet. Of course, Drain-source voltage and continuous drain current are always higher than the operation max voltage and continuous current. Basically, I am always confused about Gate-Threshold Voltage and rDS(on). Can you please clarify these points for me please with the examples? Is there any recommendation on what mosfet can fit my system?

  • +1
    TI__Guru 57737 points

    Hi Zaf,

    Welcome to e2e!

    Firstly, I would recommend you to have a look at our latest device - LM74502 instead of LM5060 for your application. LM74502 has integrated input reverse polarity protection along with UVLO and OV Protection.  In case short circuit/ over current protection is required, please have a look at TPS4811-Q1. 

    A1: Please refer https://www.ti.com/tool/TIDA-01167 design for more details. Voltage rating of these diodes is more important than the current rating as these path don't carry high current, 100mA to 200mA current capable diodes are good enough.

    A2: For Mosfet selection guidelines please refer to section '8.2.1.2.4 MOSFET Selection' of the datasheet. 

    VGS(th) - Gate-to-Source Threshold Voltage - is the voltage required to be applied across the MOSFET gate and source for current to start flowing in the MOSFET channel. At this point even though the MOSFET allows current to flow through it, the resistance of the MOSFET channel will be high. As the voltage across the MOSFET  gate and source is increased beyond VGS(th) , the channel resistance increases. After a certain point, the resistance doesn't reduce further even with increase in  VGS. This lowest resistance is called RDS(ON).