In summary, Renesas PWM D/A converters offer very high resolution (14-bits is typical) which is much higher than the 8-bit resolution of most MCU on-chip D/A converters. By using a low-pass filter at the output of a PWM D/A, even a simple RC design, the analog output is basically Vout=Vcc x Duty Cycle.  Reducing resolution to 12-bits divides it by four which also reduces the conversion time by a factor of 4. Similarly, a further factor-of-4 savings in conversion time can be achieved by reducing the resolution to 10-bits. One thing to note is that conversion time varies with the processor clock and the processor performance will “track” conversion time.