Specifications

Section 43. High-Speed PWM

High-Speed PWM

Figure 43-39: Leading-Edge Blanking

43.11.2 Individual Time Base Capture

Each PWM generator has a Primary PWM Time Base Capture register (PWMCAPx) that

automatically captures the independent time base counter value when the rising edge of the

current-limit signal is detected. This feature is active only after the application of the LEB function.

The user-assigned application should read the register before the next PWM cycle causes the

capture register to be updated again.

The Capture register is used in current-limit PWM control applications that use the analog

comparators or external circuitry to terminate the PWM duty cycle or period. By reading the

independent time base value at the current threshold, the user-assigned application can

calculate the slope of the current rise in the inductor. The secondary independent time base does

not have an associated Capture register.

43.11.3 Dead-Time Compensation

In AC motor control applications, when the dead time is applied to the PWM signals, the

transistors are disabled. During the dead time, motor current continues to flow through the

recirculating diodes, but the applied voltage is zero. The zero applied voltage during dead time

causes a distortion of the desired voltage waveform and subsequently, a motor current distortion.

This distortion causes torque variations that can affect the stability of the control system and the

performance of the motor. When Dead-Time Compensation mode is selected through the

DTC<1:0> bits (PWMCONx<7:6>), an external input signal, DTCMPx, will cause the value in the

DTRx register to be added to, or subtracted from, the duty cycle specified by the MDC/PDCx

registers. The ALTDTRx register will specify the dead-time period for both the PWMxH and

PWMxL output signals. Dead-time compensation is available only for Positive Dead-Time mode.

Negative dead times are not supported with compensation. Figure 43-40 illustrates the

dead-time compensation timing diagram.

Switching Noise

Blanking time is determined by the

LEB<9:3> bits in the LEBCONx registers

Fault and current-limit

circuitry ignores the

switching noise

PWM Output

High Power Signal

Blanking Signal

Power signal as seen

by fault circuitry