MC68HC708MP16 Datasheet, PDF (149/398 Pages) Freescale Semiconductor, Inc – Microcontrollers

Pulse Width Modulator for Motor Control (PWMMC)
9.6.3 Top/Bottom Correction
In a half-bridge AC motor drive, either the top or the bottom transistor
controls the output voltage at any given time. The direction of the motor
current determines which transistor controls the output.
POSITIVE CURRENT
NEGATIVE CURRENT
Figure 9-17. Current Convention
During deadtime, both transistors in a half-bridge are off, allowing the
load voltage to float and introducing distortion in the output voltage.
DESIRED
LOAD VOLTAGE
DEADTIME
PWM TO TOP
TRANSISTOR
POSITIVE
CURRENT
PWM TO BOTTOM
TRANSISTOR
POSITIVE CURRENT
LOAD VOLTAGE
NEGATIVE CURRENT
LOAD VOLTAGE
Figure 9-18. Deadtime Distortion
MC68HC708MP16 — Rev. 3.1
Freescale Semiconductor Pulse Width Modulator for Motor Control (PWMMC)
NEGATIVE
CURRENT
Technical Data
149