The DPWM module represents one complete DPWM channel with 2 independent outputs, A and B. Multiple DPWM modules within the UCD3138 system can be configured to support all key power topologies. DPWM modules can be used as independent DPWM outputs, each controlling one power supply output voltage rail. It can also be used as a synchronized DPWM—with user selectable phase shift between the DPWM channels to control power supply outputs with multiphase or interleaved DPWM configurations.

The output of the filter feeds the high resolution DPWM module. The DPWM module produces the pulse width modulated outputs for the power stage switches. The compensator calculates the necessary duty ratio as a 24-bit number in Q23 fixed point format (23 bit integer with 1 sign bit). This represents a value within the range 0.0 to 1.0. This duty ratio value is used to generate the corresponding DPWM output ON time. The resolution of the DPWM ON time is 250 psec.

Each DPWM module can be synchronized to another module or to an external sync signal. An input SYNC signal causes a DPWM ramp timer to reset. The SYNC signal outputs—from each of the four DPWM modules—occur when the ramp timer crosses a programmed threshold. In this way the phase of the DPWM outputs for multiple power stages can be tightly controlled.

The DPWM logic is probably the most complex of the Digital Peripherals. It takes the output of the compensator and converts it into the correct DPWM output for several power supply topologies. It provides for programmable dead times and cycle adjustments for current balancing between phases. It controls the triggering of the EADC. It can synchronize to other DPWMs or to external sources. It can provide synchronization information to other DPWMs or to external recipients. In addition, it interfaces to several fault handling circuits. Some of the control for these fault handling circuits is in the DPWM registers. Fault handling is covered in the Fault Mux section.

Each DPWM module supports the following features:

• Dedicated 14 bit time-base with period and frequency control
• Shadow period register for end of period updates.
• Quad-event control registers (A and B, rising and falling) (Events 1 to 4)
  • Used for on/off DPWM duty ratio updates.
• Phase control relative to other DPWM modules
• Sample trigger placement for output voltage sensing at any point during the DPWM cycle.
• Support for two independent edge placement DPWM outputs (same frequency or period setting)
• Dead-time between DPWM A and B outputs
• High Resolution capabilities – 250 ps
• Pulse cycle adjustment of up to ±8.192 µs (32768 × 250 ps)
• Active high/ active low output polarity selection
• Provides events to trigger both CPU interrupts and start of ADC12 conversions.