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CSD13385F5: MOSFET basics: how come this FET only has unidirectional gate-source diode?

Southern Engineering
Intellectual 635 points
Part Number: CSD13385F5
Other Parts Discussed in Thread: CSD13383F4

Hi,

I am rather used to seeing bi-directional diodes (like two Zeners facing each other) between gate and source in MOSFETs. However, this part has a uni-directional diode.

1) How come?
2) In what way would you say I should take this into consideration when selecting whether to use this part? In this case I am planning to use this nFET to switch on/off a high-side pFET (grounding/not grounding its gate) acting as a load switch.

Thanks!

  • 0
    TI__Mastermind 29525 points

    Hi Carl,

    TI makes FETs with single-ended and back-to-back (the ones you're used to seeing) ESD protection diodes. Please see the CSD13383F4 for an example of the B2B diodes. The main drawback of the B2B diodes is the gate-source leakage current, is much higher. This can be a disadvantage for battery operated systems as it can discharge the battery more rapidly in the standby state. The main thing to watch out for with the single-ended diode is any condition that may cause the gate-source diode to become forward biased. You may notice that the internal gate resistance, RG, is typically higher (240ohms) for the single-ended implementation which limits the current when the diode is forward biased. You can also add an external gate resistor if the internal one is not sufficient. If your application never causes the diode to be forward biased, then you should be OK.