SNIU028D February 2016 – September 2020 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
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.
The Sample Trigger signals are used to trigger the Front End to sample input signals. The Blanking signals are used to blank fault measurements during noisy events, such as FET turn on and turn off. This prevents false detection of faults caused by noise. They only affect the Cycle By Cycle (CBC) module. Other faults are not blanked.
Note that Sample Trigger 1 and 2, Blanking A and B, and Phase Trigger are shown at logical locations for this specific mode, but they can be placed anywhere within the period.