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I was looking for reverse voltage protection circuits for my circuit. I happen to stumble upon an IC LM74610 combined with a NMOS seems to offer a good Reverse voltage protection. As i am skimming through the datasheet to see if it can work within my system, there is this term that they advertise "Zero Iq". what does this mean? are there circuits that dont want this or is a a general good thing for all circuits?

Also why is RVP always placed on the positive end of the source of power?

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  • \$\begingroup\$ Iq = Quiescent current( "stand-by") to GND. \$\endgroup\$
    – G36
    Commented Feb 5, 2020 at 18:15

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It means that the device draws zero steady-state quiescent current from the supply. It has no connection to ground, so there's no path for even a leakage current to flow.

However, it does use energy from the source to run the charge pump and turn on the NFET gate. It does this at startup by using the voltage across the body diode to run the charge pump, and again whenever the gate voltage drops to a lower threshold.

(At that time the device turns the gate off for a short time to allow the charge pump to bring the voltage up again.)

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  • \$\begingroup\$ Assuming that the supply is perfectly at a stable voltage, the voltage after the RVP will somewhat be kind of "switching" ? So i have to choose a mosfet that is "fully on" at the highest and lowest voltage threshold of the IC? \$\endgroup\$
    – Jake quin
    Commented Feb 5, 2020 at 18:26
  • \$\begingroup\$ Correct, the FET should be of an acceptable RDSon in the min/max range of the drive thresholds. Note that the gate leakage is typically pretty small, on the order of 1uA so the part should stay on for a long time before having to refresh. \$\endgroup\$
    – John D
    Commented Feb 5, 2020 at 19:03
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I_q means "quiescent current" in this context and it's the current drawn while operational but not under load, see page 5 of the datasheet you linked. In general the lower I_q, the better, because the efficiency will be higher.

Check some background info on I_q here: http://www.ti.com/lit/an/slyt412/slyt412.pdf

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