Specifications

Tpwm=800ns

324ns

30 31 32 33 34

10nssteps

37.5%

38.8%

40.0%

41.3%

42.5%

Demanded

duty(40.5%)

EPWM1A

0 79

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Operational Description of HRPWM

2.3.1 Edge Positioning

In a typical power control loop (e.g., switch modes, digital motor control [DMC], uninterruptible power

supply [UPS]), a digital controller (PID, 2pole/2zero, lag/lead, etc.) issues a duty command, usually

expressed in a per unit or percentage terms. Assume that for a particular operating point, the demanded

duty cycle is 0.405 or 40.5% on time and the required converter PWM frequency is 1.25 MHz. In

conventional PWM generation with a system clock of 100 MHz, the duty cycle choices are in the vicinity of

40.5%. In Figure 5, a compare value of 32 counts (i.e., duty = 40% ) is the closest to 40.5% that you can

attain. This is equivalent to an edge position of 320 ns instead of the desired 324 ns. This data is shown in

Table 4.

By utilizing the MEP, you can achieve an edge position much closer to the desired point of 324 ns.

Table 4 shows that in addition to the CMPA value, 22 steps of the MEP (CMPAHR register) will position

the edge at 323.96 ns, resulting in almost zero error. In this example, it is assumed that the MEP has a

step resolution of 180 ps.

Figure 5. Required PWM Waveform for a Requested Duty = 40.5%

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

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