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TL594　High duty operation

K.Hamamoto
Guru 12155 points

Hi

Our customer will use this device at high duty condition. However the max duty of this device is defined 45%(max) at datasheet.

Is the following configuration possible? 

  - At push-pull operation, Output1(C1) and Output2(C2) is connected to same MOSFET.

  - At this configuration, the MOSFET turns on 2 times at one period.

  - Output1 ; High = 45%, Low=5% @10kHz

     OUtput2 ; Low = 5% , High =45% @10kHz

 - This means Duty-max is 90% @20kHz

Please let me know if you have any question.

Regards,

Koji Hamamoto

  • 0
    TI__Mastermind 25235 points

    Hello Koji-san,

    This 45% maximum is dependent upon the operation of the device in push pull mode.

    When the output control line is connected to the reference, the device is operating in push pull mode because the pulse steering flip flop is activating each of the transistors at separate times. The dead time control is to ensure that 

    When the output control line is connect to ground, each output transistor can operate up to 90% because the pulse steering flip flop is overridden by the output control signal.

    When considering the push pull mode of operation, the dead time control always happens at the beginning of the cycle. If we assume dead time control is set such that it is 5%, and the outputs are on the full length of time alternating between the outputs then you would have the following:

    Output 1 ON 45%, OFF 5% @ 10kHz

    Output 2 On 45%, OFF 5%  @ 10kHz

    The 5% will always be between when one of them turns off and the other turns on.

    This means Duty cycle is 90% at 20kHz as you mentioned.

    I hope this helps.

    Best,
    Michael

  • 0 in reply to Michael J Schultis
    Guru 12155 points

    Hi Michael-san

    Thank you very much for your support.

    Please let me make sure about your advice.

    1. OUTPUT CTRL = 0V,  each output can operate up to 90%

    2. OUTPUT CTRL = VREF, each output can operate up to 45%@10kHz. (minimum of dead time is 5%@10kHz.  DTC=0V)

         So, output 1 : ON=45%, OFF=5% @10kHz 

                output2 :  ON=45%, OFF=5% @10kHz

               Total : 90% @20kHz

    Is that correct?

    Regards,

    Koji Hamamoto

  • 0 in reply to K.Hamamoto
    TI__Mastermind 25235 points
    Koji-san,

    Yes, that is correct.

    Best,
    Michael
  • 0 in reply to Michael J Schultis
    Guru 12155 points

    Hi Michael-san

    I appreciate your quick reply.

    Please let me ask one more question.

    As you mentioned, the dead time is 5%@10kHz. (On the datasheet, it is mentioned that the dead time control provides 5%-100%)

    Is that dead time(5%) only for 10kHz? or Does the dead-time control provide 5%-100% at each frequency which is set by RTpin resistor?

    Regards,

    Koji Hamamoto

  • 0 in reply to K.Hamamoto
    TI__Mastermind 25235 points
    Koji-san,

    Yes, the dead time control is 5%, and that will be for the frequency which is set by Rt and Ct.

    Best,
    Michael