High-Side Drv
Controls the gate of a high-side power MOSFET relative to its moving source terminal. An N-channel device needs suitable positive gate-to-source voltage even when that source rises above ground. The driver voltage, current, timing and protection must match the selected MOSFET and circuit.
A bootstrap circuit charges a capacitor while the switching node is low enough and a charging path is available. The charged capacitor then floats with the source and supplies the high-side gate driver. Its charge is finite, so an ordinary bootstrap needs refresh opportunities. A suitable charge pump or floating supply can support operating conditions that a bootstrap alone cannot.
In plain terms
Like a carrier pigeon flying drive voltage to a stagehand on a rooftop — ground-side power can't reach the lifted source, so a small flying capacitor brings just enough charge each cycle.
Why designers use it
- Allows an N-channel power MOSFET to operate in a high-side position.
- Provides gate charging and discharging current beyond what a small logic output may provide.
- Supports half-bridge, H-bridge and other switching circuits when the driver's timing and voltage capabilities fit.
- Offers bootstrap, charge-pump or isolated-supply approaches with different duty-cycle and supply requirements.
Best for
- Sync rectifiers
- Hot-swap
- Solid-state relays
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- When the selected driver cannot produce the required gate-to-source voltage or meet device limits.
- When its refresh, isolation, timing or supply requirements do not match the application.
- Assuming a P-channel high-side switch needs only a resistor and a GPIO: a level-shift stage may be required when the supply exceeds the logic rail.
Common mistakes
- Assuming turning the high-side switch off always provides a valid bootstrap recharge path.
- Expecting an ordinary bootstrap supply to hold the gate on indefinitely without refreshing.
- Choosing gate voltage from the MOSFET threshold rather than its on-resistance and gate-voltage limits.
- Ignoring gate-loop inductance, switching transients, Miller coupling or required dead time.
- Assuming a charge-pump label guarantees every possible duty cycle, startup condition or load.
Where you will find it
- Nexperia's application note illustrates a bootstrap driver in a half-bridge, where the low-side circuit provides the capacitor recharge opportunity. It also shows charge-pump and isolated-drive alternatives for different operating requirements.
A short history
Driving an N-channel MOSFET as a high-side switch requires gate voltage above the supply rail, since the source rises toward the rail when the switch turns on. A bootstrap circuit commonly addresses this: a capacitor charges when the switching node is pulled low, then floats above the rail to supply gate drive once the switch turns on, typically needing periodic recharging through regular switching.
Good to know
- The relevant gate voltage moves with the source; it is not just a fixed voltage above ground.
- A bootstrap capacitor is a temporary floating power supply, not an unlimited voltage source.