4.2.3.3 Duty Cycle Range Limitation
In high resolution mode, the MEP is not active for 100% of the PWM period. It becomes operational:
• 3 SYSCLK cycles after the period starts when high-resolution period (TBPRDHR) control is not enabled.
• When high resolution period (TBPRDHR) control is enabled via the HRPCTL register:
– In up-count mode: 3 SYSCLK cycles after the period starts until 3 SYSCLK cycles before the period ends.
– In up-down count mode: when counting up, 3 cycles after CTR = 0 until 3 cycles before CTR = PRD, and
when counting down, 3 cycles after CTR = PRD until 3 cycles before CTR = 0.
To better understand the useable duty cycle range, see
. Duty cycle range limitations are illustrated in
. This limitation imposes a duty cycle limit on the MEP. For example, precision edge
control is not available all the way down to 0% duty cycle. When high-resolution period control is disabled,
although for the first three cycles, the HRPWM capabilities are not available, regular PWM duty control is still
fully operational down to 0% duty. In most applications, this should not be an issue as the controller regulation
point is usually not designed to be close to 0% duty cycle. When high-resolution period control is enabled
(HRPCTL[HRPE]=1), the duty cycle must not fall within the restricted range. Otherwise, there may be undefined
behavior on the ePWMxA output.
Table 4-5. Duty Cycle Range Limitation for 3 SYSCLK/TBCLK Cycles
PWM Frequency
(kHz)
3 Cycles
Minimum Duty
3 Cycles
200
0.67%
99.33% 99.00%
400
1.33%
98.67%
600
2.00%
98.00%
800
2.67%
97.33%
1000
3.33%
97.67%
1200
4.00%
96.00%
1400
4.67%
95.33%
1600
5.33%
95.67%
1800
6.00%
94.00%
2000
6.67%
93.33%
(1)
System clock - T
SYSCLKOUT
= 11.1 ns System clock = TBCLK = 90 MHz
(2)
This limitation applies only if high-resolution period (TBPRDHR) control is enabled.
T
PWM
EPWM1A
0
TBPRD
3
SYSCLKOUT =
TBCLK
Figure 4-7. Low % Duty Cycle Range Limitation Example (HRPCTL[HRPE] = 0)
High-Resolution Pulse Width Modulator (HRPWM)
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
387
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Содержание TMS320 2806 Series
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