TMS320F28335: Maximum switching frequency for TMS320F28335

500kHz PWM freq is fine.

For delay in close loop what is your sampling frequency? That will be the delay in your loop.

For open loop the delay does not apply.

ADC conversion delay does not change with sampling frequency. That is fixed by ADC clock which is much higher CPU system clock. ADC delay in this case is 80nS.

Your 1 MHz sampling loop will cause a 1uS delay because this is the rate at which feedback signal is sensed by ADC, then control output is calculated in ISR and PWM is updated accordingly

Max switching freq can be about 1MHz. But at that freq you will have to use HRPWM. If the freq is 250kHz or lower then normal PWM resolution (6.67nS) should be fine

Pls check Datasheet for the ADC max sampling speed of this MCU.