IXYS Corporation Power MOSFETs

Trench and planar MOSFETs differ in structure and performance characteristics: (1) Trench MOSFETs - vertical channel structure provides higher cell density, lower Rds(on), and better for low-voltage (<200V) applications

(2) Planar MOSFETs - horizontal channel structure offers better high-voltage capability (>500V) and avalanche ruggedness. IXYS offers both technologies: TrenchFET series for low-voltage high-current applications, X-Class series for high-voltage applications. Trench devices typically have lower gate charge for faster switching, while planar devices offer superior body diode performance.

Choose trench MOSFETs for low-voltage high-current; planar MOSFETs for high-voltage applications.

MOSFET power dissipation consists of conduction and switching losses: (1) Conduction loss - Pcond = I² × Rds(on) × duty cycle. Use Rds(on) at actual operating temperature (typically 1.5-2x 25°C value)

(2) Switching loss - Psw = 0.5 × V × I × (tr + tf) × fsw, where tr/tf are rise/fall times, fsw is switching frequency

(3) Gate drive loss - Pgate = Qg × Vgs × fsw

(4) Total loss - Ptotal = Pcond + Psw + Pgate. Ensure total dissipation is within thermal limits: Tj = Ta + (Ptotal × Rth(j-a)). IXYS datasheets provide thermal and switching characteristics for accurate calculations.

Calculate both conduction and switching losses at worst-case conditions to ensure reliable operation.

Avalanche rating (EAS - Single Pulse Avalanche Energy) indicates a MOSFET's ability to withstand unclamped inductive switching events: (1) Definition - energy the device can absorb when switching off an inductive load without external clamping

(2) Importance - protects against voltage transients in motor drives, solenoids, and relay applications

(3) Rating - specified in millijoules (mJ) at specific current and starting temperature

(4) IXYS advantage - many IXYS MOSFETs feature robust avalanche capability, eliminating need for external protection components. Always ensure EAS rating exceeds worst-case energy in your application.

Select MOSFETs with adequate avalanche rating for inductive load applications to eliminate external protection.

Temperature significantly impacts MOSFET characteristics: (1) Rds(on) increases with temperature - typically 0.3-0.5% per °C, meaning 50-80% higher at 125°C vs 25°C

(2) Gate threshold voltage decreases - approximately -7mV/°C

(3) Switching speed may decrease slightly at high temperatures

(4) Maximum current decreases due to higher thermal resistance. Design considerations: (1) Size for worst-case Rds(on) at maximum junction temperature

(2) Ensure adequate heatsinking for continuous operation

(3) Consider derating for high ambient temperatures. IXYS datasheets provide normalized curves for temperature effects.

Always design using maximum Rds(on) at worst-case junction temperature, not the 25°C datasheet value.

Proper gate drive is critical for MOSFET performance: (1) Drive voltage - use 10-15V for standard MOSFETs, 5V for logic-level devices

(2) Gate resistor - controls switching speed and EMI

typical values 5-50Ω depending on switching frequency

(3) Drive current - must charge/discharge gate capacitance quickly

Ig = Qg/t, where t is desired switching time

(4) Miller plateau - ensure drive can supply plateau current for fast switching

(5) Negative voltage - consider -3 to -5V for high-power applications to prevent false turn-on. IXYS provides recommended gate drive circuits in application notes.

Design gate drive with adequate voltage, current capability, and proper gate resistance for your switching frequency.