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UCC27201A: Max Duty

Part Number: UCC27201A


May I know the max duty of UCC27201A? 


  • Hi Jack, 

    Could you please provide more details? The high side channel won't support 100% duty cycle applications since it is biased by the bootstrap capacitor which needs to be recharged at each cycle. 

    Best regards, 


  • Hi Leslie, 

    Thank you for the swift reply. 

    The use of the device is for battery backup unit application. 

    Please correct me if I am wrong. A bootstrap capacitor on a low VF won't reach 100% duty cycle. How about a high VF? What is the max duty cycle UCC27201A can reach? 

    Thank you. 


  • Hi Jack, 

    Are you looking for 100% duty cycle on the high side channel? This FAQ talk about 100% duty cycle:

    Otherwise, if you are just looking for a high duty cycle for the high side channel, but not 100%, how long you can keep the high side channel ON during each cycle will depend on how long the bootstrap capacitor can stay charged above HB UVLO. These are the things that discharge the bootstrap capacitor:

    1. Charging of the FET’s Qg (Immediate drop, happens during rising time of the driver’s output)
      • Using Q=C*V, the immediate voltage drop is V=Q/C, where:
        • “Q” is the FET’s gate charge
        • “C” is the capacitance of the bootstrap capacitor
        • “V” is the immediate voltage drop on the bootstrap capacitor due to charging of the FET’s Qg
    2. HB quiescent current (It will slowly discharge the bootstrap capacitor during long times)
      • Using IT=CV, the voltage drop due to the HB quiescent current in a specific time interval is V=IT/C, where:  
        • “I” is the HB quiescent current of the driver
        • “T” is the time it takes for the capacitor to discharge to “V” level
        • “V” is the voltage drop in the capacitor after “T” time interval
        • “C” is the capacitance of the bootstrap capacitor

      The addition of the immediate voltage drop calculated in #1 and the voltage discharge over time calculated in #2 should not exceed the allowable voltage drop on HB pin to ensure that the high side driver stays above UVLO. If a gate to source resistor is used this will also provide a path for the capacitor to discharge and it can be calculated the same way as done for the HB quiescent current (#2 above). 

      Best regards,


    1. I see. thank you for your great support.