Texas Instruments TMS320 2833 Series User Manual

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
www.ti.com Operational Description of HRPWM
331
SPRUI07–March 2020
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High-Resolution Pulse Width Modulator (HRPWM)
4.2.3.1 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 4-5, a compare value of 32 counts (that is, 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 4-4.
By utilizing the MEP, you can achieve an edge position much closer to the desired point of 324 ns.
Table 4-4 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 4-5. Required PWM Waveform for a Requested Duty = 40.5%
(1)
System clock, SYSCLKOUT and TBCLK = 100 MHz, 10 ns
(2)
For a PWM Period register value of 80 counts, PWM Period = 80 x 10 ns = 800 ns, PWM frequency = 1/800 ns = 1.25 MHz
(3)
Assumed MEP step size for the above example = 180 ps
See the device-specific data manual for typical and maximum MEP values.
Table 4-4. CMPA vs Duty (left) and [CMPA:CMPAHR] vs Duty (right)
CMPA
(1) (2) (3)
(count)
DUTY
%
High Time
(ns)
CMPA
(count)
CMPAHR
(count)
Duty
(%)
High Time
(ns)
28 35.0 280 32 18 40.405 323.24
29 36.3 290 32 19 40.428 323.42
30 37.5 300 32 20 40.450 323.60
31 38.8 310 32 21 40.473 323.78
32 40.0 320 32 22 40.495 323.96
33 41.3 330 32 23 40.518 324.14
34 42.5 340 32 24 40.540 324.32
32 25 40.563 324.50
Required 32 26 40.585 324.68
32.40 40.5 324 32 27 40.608 324.86

Texas Instruments TMS320 2833 Series Specifications

General

Brand	Texas Instruments
Model	TMS320 2833 Series
Category	Controller
Language	English