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Topic: High side NMOS gate driver recommendations (Read 966 times) previous topic - next topic


Hi all,

I've got some high side p-channel MOSFETs providing high side general purpose power switches from a board I'm working on, but as mentioned to me in a thread - you can of course use NMOS if you've got a high enough voltage available for the gate relative to source (why it took somebody to tell me this as opposed to me seeing it is besides the point :D)

Can anybody a) recommend a high sided NMOS gate driver, as the obvious ones such as the MAX1614 seem to be aimed at power distribution applications in devices such as phones etc, and so have multiple pins for other purposes I don't need.

and b) or alternatively, can I not just use a DC-DC converter to give me the voltage I need (appropriately sized for switching current of course) to drive NMOS gates on the high side?


Do you want to switch static loads? (most high-side drivers require a constant PWM signal to drive
the bootstrap suuply)

The Intersil chips like HIP4081 and HIP4086 have a charge-pump that allows the high side gate drive
to be constantly on without problems (but don't add a gate-pulldown, its a very weak charge-pump).

They are good to 80V.   the '4081 is a full-bridge (2 high, 2 low drivers) and the '4086 is a three-phase bridge
(3 high, 3 low drivers).  They put out an amp or so of gate drive so cope with even very large MOSFETs.

[ I won't respond to messages, use the forum please ]


I'll be switching both static and/or PWM depending... The chips recommended look like a nice little device, however - a little help reading the datasheet(s) if possible - how does one know if a device is suitable for static switching, or PWM only?


Several of the HIP408x series have a charge pump circuit that can provide only a very small current,
but can provide this continually (there's an on-board oscillator I think).  I haven't seen this approach
in many other chips.

Because the current is very small the high side device must not have a gate-source pulldown
resistor unless its a very large value (or it'll cause the supply to sag).  When the low-side switch
parks in an off-state this small current is the only thing keeping the bootstrap capacitor charged.

The downside to the charge-pump circuit is that it takes power proportional to the MOSFET supply voltage
which can become the limiting factor in power-dissipation for the driver.

All high-side drivers use a bootstrap capacitor to provide drive voltage when the device is switching,
and thus all will work with PWM if its switching all the time or if it only ever stops with low-side switch
on (this means the bootstrap cap is kept charged through the diode).  The size of the bootstrap capacitor
depends on the PWM rate and the MOSFET gate total charge.
[ I won't respond to messages, use the forum please ]

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