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UCC28950: To know the min switching frequency and max resistance on RAB/RCD

Eric Lai
Expert 4940 points
Part Number: UCC28950

Hi Expert,

The engineer would like to run the switching frequency lower than 50Khz and set the resistance over 90K on RAB/RCD .   

Pls advice the limitation for min frequency and max resistance of RAB/RCD.

Thanks

Best regards,

Eric Lai

  

Field Application Engineer

Texas Instruments Taiwan Limited

O: +886-2-2175-2582

M: +886-909-262-582

E-Mail:Eric.Lai@ti.com         

  • 0
    TI__Mastermind 25570 points

    Hello Eric

    The upper limit of 90k on RAB and RCD was set by considerations of noise sensitivity. The controller will operate with resistors greater than this limit but TI will not recommend doing this. 90k will set a delay of 1.5us and this should be sufficient for all normal purposes - I'd appreciate if you can let me know why the engineer thinks the power stage requires delays greater than this.

    The minimum switching frequency of 50kHz is also set by considerations of accuracy - you can see from Fig 35 of the Data Sheet.

    One possibility would be to set the free running frequency at 50kHz, configure the controller as a SLAVE (Timing resistor from RT pin to GND) and to use an external 90kHz source to sync the controller down to 90% of 50kHz (45kHz).

    Let me know if the customer wants to run at a lower frequency than this.

    Regards

    Colin