One I missed: OnSemi NCV68261 ideal diode and high-side switch

And, being partial to a nice ideal diode, I thought I would take a look.

It is a neat chip, called NCV68261 and measuring 2 x 2mm.

Acting on the high-side, it is designed to work with an external n-channel mosfet, or two mosfets if load switching is required.

A charge pump inside provides a voltage above the most positive rail with which to switch the mosfet gate or gates.

It can either:

• Be a diode and protect against reverse polarity connections AND against reverse current flow
  (top diagrams, ‘D’ connected to output)…
• Or just protect against reverse polarity connections, but not against reverse current flow
  (bottom diagrams, ‘D’ connected to ground)

The crucial ‘Vin – D’ thresholds for reverse current switching (there is a comparator inside) are +100 to +220mV (140mV typ) rising, and -40 to 0mV (-10mV typ) falling. According to OnSemi: “In general, any NMOS can be connected to the NCV68261….. the gate to source maximum voltage of the transistor should be rated above a 15 V level.”

I suspect that the Rds(on) is also important, as that -40mV needs to be generated by the reverse flow through the mosfet for the device to always turn off – unless I am misreading how it works.

The max gate drive of 15V is with >8V on the circuit input.

If the input is 4V, the drive voltage is typically 4V, (3Vmin) but no maximum is given – naughty OnSemi.

The device has been designed to be compatible with automotive rails, but also industrial applications: operation is over 3 to 32V, but the device, said On, is immune to 60V load-dump pulses and disconnects the load if Vin≥35.6V typ.

It is also immune to -40V transients, and the under voltage threshold is typically +3.4V.

Consumption is 295μA max and typically 210μA, dropping to 5μAtyp when disabled.

Find the NCV68261 data sheet here

*No, THIS is the best reverse polarity protection circuit! by Hasse Industries, on YouTube.
BTW, I don’t agree with the presenter’s assertion that this is better than a p-channel mosfet in the positive rail (with optional Zener and resistor if the gate needs it) – or n-channel in the negative rail – for reverse-polarity protection, but it is a nice ideal diode if reverse flow protection is needed too.