Pulse 280 Specifications download pdf (Page 7)

PWM

SYSCLK

PWMresolution(%)=F /F x100%

PWM SYSCLKOUT

PWMresolution(bits)=Log (T /T )

2 PWM SYSCLKOUT

Reference Guide

SPRU924F– April 2005– Revised October 2011

High-Resolution Pulse Width Modulator (HRPWM)

This document is used in conjunction with the device-specific Enhanced Pulse Width Modulator (ePWM)

Module Reference Guide.

The HRPWM module extends the time resolution capabilities of the conventionally derived digital pulse

width modulator (PWM). HRPWM is typically used when PWM resolution falls below ~ 9-10 bits. This

occurs at PWM frequencies greater than ~200 kHz when using a CPU/system clock of 100 MHz. The key

features of HRPWM are:

• Extended time resolution capability

• Used in both duty cycle and phase-shift control methods

• Finer time granularity control or edge positioning using extensions to the Compare A and Phase

registers

• Implemented using the A signal path of PWM, i.e., on the EPWMxA output. EPWMxB output has

conventional PWM capabilities

• Self-check diagnostics software mode to check if the micro edge positioner (MEP) logic is running

optimally

1 Introduction

The ePWM peripheral is used to perform a function that is mathematically equivalent to a digital-to-analog

converter (DAC). As shown in Figure 1, where T

SYSCLKOUT

= 10 ns (i.e. 100 MHz clock), the effective

resolution for conventionally generated PWM is a function of PWM frequency (or period) and system clock

frequency.

Figure 1. Resolution Calculations for Conventionally Generated PWM

If the required PWM operating frequency does not offer sufficient resolution in PWM mode, you may want

to consider HRPWM. As an example of improved performance offered by HRPWM, Table 1 shows

resolution in bits for various PWM frequencies. These values assume a 100 MHz SYSCLK frequency and

a MEP step size of 180 ps. See the device-specific datasheet for typical and maximum performance

specifications for the MEP.

Table 1. Resolution for PWM and HRPWM

PWM Freq Regular Resolution (PWM) High Resolution (HRPWM)

(kHz)

Bits % Bits %

20 12.3 0.0 18.1 0.000

50 11.0 0.0 16.8 0.001

100 10.0 0.1 15.8 0.002

SPRU924F– April 2005– Revised October 2011 High-Resolution Pulse Width Modulator (HRPWM)

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