To realize totem-pole modulation, compare the output error signal of current loop with the generated sawtooth wave. See Table 2-2 for the switching state. The positive and negative values of the error signal determine the switching state of the low-frequency bridge, and the intersection point between the sawtooth and error signals determines the switching state of the high-frequency bridge. To avoid the PWM signal glitch near the zero point, set the threshold value.

Additionally, to avoid short circuits in bridge, the dead time is set. Since a continuous sample rate is set, all these functions are executed with a certain sequence; therefore, a delay function cannot be added in the transient time. Instead, a background timer is set in the update function and accumulates every sample time. Therefore, once the counter reaches the desired value, the timer turns off or turns on another FET in the bridge. Accordingly, the turn-on or turn-off time can be extended, but cannot be decreased to achieve dead-time control. Figure 3-13 and Figure 3-14 show the codes.

Figure 3-13 Background Dead-Time Counter in Update Function

Although the counter number is set to 11, the effective number is 10 which means the dead time is 83.3ns.

Figure 3-14 Totem-Pole Control Code in Positive Cycle