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Max switching frequency to achive with C2000 controllers

Caglar Cihan
Expert 6235 points


Dear Team,

One of my customers would like to build Phase Shifted Full Bridge power supply at below given specifications:

Input Voltage Range : Universal AC ( 85 -264 VAC)

Output Voltage : 24VDC

Output Power : 1kW

They are planning to use GaN switches to be able to increase the switching frequency but they are not sure about the max practical achiable switching frequency with our C2000 controllers.

Is HRPWM modules capable of driving GaN switches in 500kHz to 1MHz range? If so, which product family could  be a better fit for this application?

Best Regards,

Caglar

  • 0
    TI__Mastermind 27200 points
    Caglar,

    There isn't a simple answer to this question. As the switching frequency increases there will be a progressive loss of PWM edge resolution because the PWM clock is positioned by a counter typically clocked at the (fixed) CPU frequency. This in turn leads to loss of control accuracy, and ultimately to issues such as limit cycling. The attached slides illustrate the situation.

    Whether limit cycles appear or not depends on more than just PWM edge resolution. Factors such as the plant gain, ADC resolution, and numerical gain through the controller, all play a role.

    To mitigate the problem the C28x PWM architecture includes a "high resolution" (HR) mode which allows edges to be positioned with a temporal accuracy of about 180 ps. This is often sufficient to ensure good control at frequencies beyond 1 MHz, but again, it depends on the system. HR mode can be applied to PWM duty cycle, frequency, and (importantly in the case of the phase shifted full bridge topology) phase shift between PWM channels.

    If current mode control is being used, the PWM resolution doesn't matter. Then, the resolution limit comes from the internal DAC which feeds the analog comparator. This is very complicated to quantify, especially if slope compensation is applied. Regret there's aren't currently any figures I can give for that.

    There is no other platform better suited to digital control of switched mode digital power supplies.

    Regards,

    Richard