AN2281 datasheet(14/38 Pages) STMICROELECTRONICS

Part #	AN2281

Description	Low cost self-synchronizing PMAC motor drive using ST7FLITE35

PDF	38 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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14 / 38 page

Application schematics

AN2281

14/38

4.1

Gate driving and dead time insertion circuit

Figure 11 shows in detail one of the three legs of the DC-AC inverter used in the reference

schematic, with the corresponding gate driving circuit. The description of this leg is valid for

the whole inverter.

In order to drive the U4 MOSFETs correctly and to avoid their contemporary conduction, the

signal coming from the microcontroller and applied at the base of bipolar transistor Q8 is,

first of all, level shifted by the emitter follower stage (Q8) and, then, a dead time is inserted

delaying the turn-on of the NMOS and PMOS devices and by making their turn-off

instantaneous.

Referring to the control signal (applied on point B in Figure 11) low-to-high transition and

assuming the P-channel MOSFET fully turned on when |VGS|=VTH, you can compute the

dead time value by solving the following equation:

Figure 11. The dead time insertion circuit

(4.1)

VBUS=VTHp

(

)

R13*CPMOSin

1-e

AN2281 Datasheet(PDF) 14 Page - STMicroelectronics