Introduction To Dpwm (Dpwm Multi-Mode, Open Loop) - Texas Instruments UCD3138 Technical Reference Manual

www.ti.com
2.2

Introduction to DPWM (DPWM Multi-Mode, Open Loop)

The DPWM is based on a DPWM counter, which counts up from 0 to a period value, and then is reset and
starts over again. The counter can also be reset by a sync signal, either from the SYNC pin, or from
another DPWM.
The DPWM logic causes transitions in many digital signals when the period counter hits the target value
for that signal. In the Timing Module block diagram shown above, this is functionality is represented by a
digital comparator.
The DPWM has a basic 250 MHz clock, giving a resolution of 4 nanoseconds. 15 other 250 MHz clocks
are generated spaced 250 picoseconds apart. Output pulse widths and pulse spacing are controlled by
these clocks, giving a resolution of 250 picoseconds. The edges generated by these clocks are hence
referred to as "High Resolution" in the illustrations throughout this section.
Most of the signals out of the DPWM are fairly simple. The only complex signals are DPWMA and
DPWMB. These vary depending upon the power supply topology and are the most important signals
coming out of the DPWM.
The DPWM has many modes to support different topologies. These are selected by a mode bit field in a
DPWM control register. The "Multi mode, Open loop" mode is used to introduce the DPWM here, while the
other DPWM modes are described in subsequent sections.
Figure 2-3 illustrates most of the signals involved in the DPWM in a mode known as "Multi mode, Open
loop". Open loop means that the DPWM is controlled entirely by its own registers, not by the filter output.
In other words, the power supply control loop is not closed. This mode is used for introducing the DPWM
because there is a very simple correlation between DPWM register values and signal timing.
SNIU028A – February 2016 – Revised April 2016
Submit Documentation Feedback
Introduction to DPWM (DPWM Multi-Mode, Open Loop)
Copyright © 2016, Texas Instruments Incorporated
Digital Pulse Width Modulator (DPWM)
37