SchematicsHub.com

1. Why a dedicated gate driver is mandatory

A MOSFET gate is a dynamic system of capacitances: C_gs, C_gd (Miller), and C_ds. During switching, the gate driver must move charge through these non-linear capacitances fast enough to minimize time in the linear region. A typical modern MOSFET like IPP110N20N3 has a total gate charge Q_g ≈ 165 nC. If you want a 30 ns transition, the required gate drive current is:

I = Qg / t_sw ≈ 165e-9 / 30e-9 ≈ 5.5 A

No microcontroller pin can provide such current. Even “strong” GPIO drivers (20–40 mA) are 100× weaker than needed. As a result, the MOSFET spends a large fraction of each cycle in the linear region, dissipating tens of watts as heat.

2. Key MOSFET examples

2.1 IRLZ44N (55 V, 47 A, Qg ≈ 67 nC)

A classic logic-level MOSFET, still widely used in low-voltage motor and DC switching applications. With Q_g around 67 nC, it can be driven by a mid-strength gate driver at moderate frequencies, but driving it directly from GPIO is still a bad idea for anything above a few kHz.

2.2 IPP110N20N3 (200 V, 110 A, Qg ≈ 165 nC)

A high-power MOSFET for SMPS, PFC and inverter stages. Its large gate charge and high voltage rating make it ideal for half-bridge or full-bridge topologies, but only with a serious gate driver providing multiple amps of peak current.

2.3 IPT015N10N5 (100 V, 150 A, Qg ≈ 45 nC)

A modern low-charge MOSFET optimized for high-efficiency synchronous buck converters. Q_g is relatively low for the current it can handle, which allows high-frequency operation when combined with a strong driver like UCC27531.

3. Recommended driver ICs

3.1 UCC27531 (Texas Instruments)

• 2.5 A source / 5 A sink peak
• Low propagation delay (~18 ns)
• Excellent fit for low-side FETs in synchronous buck converters

UCC27531 is well suited for driving devices like IRLZ44N or IPT015N10N5 in low-side configurations, providing fast, controlled gate transitions.

3.2 IRS2007 (Infineon) – half-bridge driver

• Bootstrap high-side driver (up to 600 V)
• Integrated dead-time
• Designed for motor drives, inverters, PFC

For high-voltage half-bridges with MOSFETs such as IPP110N20N3, IRS2007 offers both high-side and low-side drive with proper level shifting and bootstrap circuitry.

3.3 FAN7392 (onsemi) – high-current half-bridge driver

• Up to 4 A peak gate drive
• Robust dv/dt performance
• Suitable for demanding SMPS and motor stages

4. Gate charge and the Miller plateau

The gate charge curve is usually more informative than static capacitances like C_iss. The critical region is the Miller plateau, where the gate voltage remains almost constant while drain voltage changes quickly.

Vgate
│         plateau (Miller)
│     ___------______
│    /
│___/
          

During this plateau, most of the energy goes into C_gd, controlling dv/dt and thus EMI and switching losses. The faster the driver can push through Q_gd, the shorter the MOSFET remains in the linear region.

5. Gate resistor: Rg, Ron and Roff

A gate resistor is mandatory to control switching speed, suppress ringing, reduce EMI and protect the driver.

• Low-power stages: 4.7–10 Ω
• Medium power: 10–33 Ω
• High power: 20–68 Ω

For demanding designs, use separate resistors for turn-on and turn-off: R_on in series with the pull-up path and R_off in series with the pull-down path, or a diode + resistor combination.

6. Kelvin source connection

The MOSFET source lead should have a separate, low-inductance return path to the driver ground:

Driver GND ──────────┐
                     │  Kelvin return
MOSFET Source ───────┘
          

This minimizes errors caused by source inductance and high di/dt, especially in half-bridge configurations.

7. Bootstrap circuits for high-side N-MOSFET

To drive a high-side N-channel MOSFET above the supply rail, a bootstrap circuit is typically used. It consists of:

• a fast recovery or Schottky diode
• a bootstrap capacitor (typically 100–220 nF)

Correct sizing of the bootstrap capacitor is essential. Too small a value leads to excessive droop during high-side conduction, causing the gate to fall below the required drive voltage.

8. Dead-time optimization

Dead-time is the interval where both high-side and low-side MOSFETs are off. Too little dead-time leads to shoot-through; too much dead-time increases losses and reduces efficiency.

• Si MOSFET: typically 50–200 ns
• GaN: typically 10–40 ns

Drivers like IRS2007 and FAN7392 offer built-in or programmable dead-time to keep this region under control.

9. Typical driver schematics

Single low-side driver (e.g. UCC27531 + IPT015N10N5)

MCU → UCC27531 → Rg → MOSFET Gate
                    ↓
                   Kelvin GND
          

Half-bridge with bootstrap (e.g. IRS2007 + IPP110N20N3)

          VB ───────┐ bootstrap
                     │
MCU → IRS2007 → HO ──┴──> High-side MOSFET
           → LO ───────> Low-side MOSFET
          

10. PCB layout rules

• Minimize gate loop area (driver–gate–source–driver)
• Route Kelvin source separately from power return
• Place driver and bootstrap parts as close to MOSFET gates as possible
• Use a solid ground plane where possible
• Use thermal vias under MOSFET pads for heat spreading

11. EMI and noise

Major EMI sources in MOSFET stages:

• high dv/dt at the switch node
• reverse recovery of diodes
• parasitic inductances in loops and leads

Mitigation techniques:

• RC snubbers across the switch node
• slightly slower gate transitions (larger Rg)
• careful dead-time tuning
• Schottky diodes to clamp undershoot

12. Debug checklist

• Measure V_gs with a ×10 or ×100 probe
• Verify Miller plateau region shape and duration
• Check for ringing above 30–50 MHz
• Verify real dead-time with an oscilloscope
• Check bootstrap voltage under full load
• Monitor driver UVLO (undervoltage lockout) behavior

13. Typical failure mechanisms

• dV/dt-induced false turn-on
• gate oxide breakdown from overshoot
• shoot-through due to insufficient dead-time
• excessive switching losses due to slow transitions
• ringing and parasitic oscillations in the gate loop

14. Conclusion

A proper MOSFET gate driver is not an optional upgrade, but a mandatory part of a modern power stage. Correct driver selection (UCC27531, IRS2007, FAN7392), matching it to real MOSFETs (IRLZ44N, IPP110N20N3, IPT015N10N5), plus solid layout and controlled gate drive will dramatically improve efficiency, reliability and lifetime of any SMPS or inverter.