Datasheet

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SLUS353C –NOVEMBER 2003–REVISED JUNE 2013 www.ti.com
For drives where speed is critical, P-Channel MOSFETs can be driven by emitter followers as shown in
Figure 10. Here, both the level shift NPN and the PNP must withstand high voltages. A zener diode is used to
limit gate-source voltage on the MOSFET. A series gate resistor is not necessary, but always advisable to control
overshoot and ringing.
High-voltage optocouplers can quickly drive high-voltage MOSFETs if a boost supply of at least 10 V greater
than the motor supply is provided (See Figure 11) To protect the MOSFET, the boost supply should not be
higher than 18 V above the motor supply.
For under 200-V 2-quadrent applications, a power NPN driven by a small P-Channel MOSFET performs well as
a high-side driver as in Figure 12. A high voltage small-signal NPN is used as a level shift and a high voltage
low-current MOSFET provides drive. Although the NPN will not saturate if used within its limitations, the base-
emitter resistor on the NPN is still the speed limiting component.
Figure 13 shows a power NPN Darlington drive technique using a clamp to prevent deep saturation. By limiting
saturation of the power device, excessive base drive is minimized and turn-off time is kept fairly short. Lack of
base series resistance also adds to the speed of this approach.
Figure 10. Fast High-Side P-Channel Driver Figure 11. Optocoupled N-Channel High-Side
Driver
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