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I'm working out a circuit for the TI bq24179 battery charger and struggling to understand the opposing mosfet symbol they are using. I've taken a screenshot of the symbol(s) below:

enter image description here

In the datasheet they refer to both the ACFET and RBFET as N-Channel Mosfets, but nothing about the diode. Is this some inherent parasitic diode in a common-source mosfet pair that I'm unaware of or an additional component I should be adding? Or does this symbol pair + diode represent some single component I don't know the name of?

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  • \$\begingroup\$ It's a zener diode, for gate overvoltage protection. \$\endgroup\$ Oct 26, 2021 at 10:38
  • \$\begingroup\$ it's an high side bidirectional load switch. And the diode usually is a zener as already stated. Any dual fet package or even two discrete fets would work \$\endgroup\$ Oct 26, 2021 at 10:58
  • \$\begingroup\$ If it is not a zener diode does it actually provide any protection? Say for example you had a mosfet with Max V_GS of 10V, 0V at the source and 15V at the gate. Wouldn't the mosfets still fry in this configuration? If it is a zener then the gate voltage would be kept constant at the zener voltage, which is what would provide the protection right? \$\endgroup\$
    – topher217
    Oct 27, 2021 at 2:12

1 Answer 1

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There is nothing too fancy about this configuration - when its ON its ON, when it's OFF it's OFF in both directions. There are many dual common-source N-MOSFETs in a single package available on the market. The diode provides some reverse Vgs protection but may not be strictly necessary depending on the maximum Vgs of the devices (but diodes are cheap). Check out the CSD87312Q3E to give you an idea, if you haven't already come across it for your application. There are many similar from other vendors depending on your power requirements etc ...

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  • \$\begingroup\$ Great! Thanks for the possible component. Is there any way to filter components on Digi-key to only include common-source common-gate like this? I was having a real hard time trying to find one like this. \$\endgroup\$
    – topher217
    Oct 26, 2021 at 9:08
  • \$\begingroup\$ I suppose I can just route them together on the PCB, and maybe I was trying to search too hard. \$\endgroup\$
    – topher217
    Oct 26, 2021 at 9:29
  • \$\begingroup\$ Need to search for dual device then by P or N and then slect the ones that may already be common gate etc. ahhh, it's a hard slog :-) \$\endgroup\$
    – citizen
    Oct 26, 2021 at 9:38
  • \$\begingroup\$ Thank you for pointing out my end-of-day exaggerations of difficulty :D. I'll go have a drink and reassess my concepts of difficulty. \$\endgroup\$
    – topher217
    Oct 26, 2021 at 9:42

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