Enhanced PWM (ePWM) Module
15.2.2.10.4 Configuring the High-Resolution PWM Submodule
Once the ePWM has been configured to provide conventional PWM of a given frequency and polarity, the
HRPWM is configured by programming the HRCNFG register located at offset address 1040h. This
register provides configuration options for the following key operating modes:
•
Edge Mode: The MEP can be programmed to provide precise position control on the rising edge (RE),
falling edge (FE), or both edges (BE) at the same time. FE and RE are used for power topologies
requiring duty cycle control, while BE is used for topologies requiring phase shifting, for example,
phase shifted full bridge.
•
Control Mode: The MEP is programmed to be controlled either from the CMPAHR register (duty cycle
control) or the TBPHSHR register (phase control). RE or FE control mode should be used with
CMPAHR register. BE control mode should be used with TBPHSHR register.
•
Shadow Mode: This mode provides the same shadowing (double buffering) option as in regular PWM
mode. This option is valid only when operating from the CMPAHR register and should be chosen to be
the same as the regular load option for the CMPA register. If TBPHSHR is used, then this option has
no effect.
15.2.2.10.5 Operational Highlights for the High-Resolution PWM Submodule
The MEP logic is capable of placing an edge in one of 255 (8 bits) discrete time steps, each of which has
a time resolution on the order of 150 ps. The MEP works with the TBM and CCM registers to be certain
that time steps are optimally applied and that edge placement accuracy is maintained over a wide range of
PWM frequencies, system clock frequencies and other operating conditions.
shows the
typical range of operating frequencies supported by the HRPWM.
Table 15-41. Relationship Between MEP Steps, PWM Frequency and Resolution
Resolution at
System
MEP Steps Per
PWM Minimum
PWM Maximum
Maximum
(MHz)
SYSCLKOUT
(1) (2) (3)
(Hz)
(4)
(MHz)
(Bits)
(5)
50.0
111
763
2.50
11.1
60.0
93
916
3.00
10.9
70.0
79
1068
3.50
10.6
80.0
69
1221
4.00
10.4
90.0
62
1373
4.50
10.3
100.0
56
1526
5.00
10.1
(1)
System frequency = SYSCLKOUT, that is, CPU clock. TBCLK = SYSCLKOUT
(2)
Table data based on a MEP time resolution of 180 ps (this is an example value)
(3)
MEP steps applied = T
SYSCLKOUT
/180 ps in this example.
(4)
PWM minimum frequency is based on a maximum period value, TBPRD = 65 535. PWM mode is asymmetrical up-count.
(5)
Resolution in bits is given for the maximum PWM frequency stated.
1553
SPRUH73H – October 2011 – Revised April 2013
Pulse-Width Modulation Subsystem (PWMSS)
Copyright © 2011–2013, Texas Instruments Incorporated