The UCC21750 features the PWM interlock for IN+ and IN– pins, which can be used to prevent the phase leg shoot through issue. As shown in Table 8-1, the output is logic low while both IN+ and IN– are logic high. When only IN+ is used, IN– can be tied to GND. To use the PWM interlock function, the PWM signal of the other switch in the phase leg can be sent to the IN– pin. As shown in Figure 9-2, the PWM_T is the PWM signal to top side switch, the PWM_B is the PWM signal to bottom side switch. For the top side gate driver, the PWM_T signal is given to the IN+ pin, while the PWM_B signal is given to the IN- pin; for the bottom side gate driver, the PWM_B signal is given to the IN+ pin, while PWM_T signal is given to the IN- pin. When both PWM_T and PWM_B signals are high, the outputs of both gate drivers are logic low to prevent the shoot through condition.

Figure 9-2 PWM Interlock for a Half Bridge