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TPS923655: delay created by the IC from PWM or Dimming input

Ernest Yong
Expert 4680 points
Part Number: TPS923655
Other Parts Discussed in Thread: TPS922055

Hi Team,

May I check what will be the delay created by the IC from PWM or Dimming input to the o/p gate toggling ? able to see this chips are supporting very narrow pulse width operation 150 ns ?

 

Customer trigger duration is 100us and our trigger current is 5 A Through the LED ,they are using it for a Flash photo capture camera 42 frames at 1000 Fps

So there should be less delay for the pulse to propagate to have good synchronized exposure ..

Just gone through the datasheet at the top level couldn’t find the information yet , please let me know if we have the data!

Many thanks!

Best Regards,

Ernest

  • 0
    TI__Mastermind 23245 points

    Hi Ernest,

    Sorry. I am currently out of office. I will reply to you before next Tuesday. Thanks for your understanding.

    Best Regards,

    Steven

  • 0
    TI__Mastermind 23245 points

    Hi Ernest,

    The minimum pulse width input at the EN/PWM pin the IC can detect is 150ns (MAX). You can check below specs from Section 7.5 Electrical Characteristics in the datasheet.

    During normal operation (after startup and after dimming mode has been selected), once a rising / falling edge at the EN/PWM pin is detected by the IC, the IC will start / stop switching immediately without any delay.

    Ernest Yong said:
    May I check what will be the delay created by the IC from PWM or Dimming input to the o/p gate toggling ?

    May I understand what the "o/p" refers to? Does it refer to output?

    It is possible for TPS923655 to achieve 100us pulse if the external components are well selected. May I understand what your input voltage, LED voltage and current are?

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    TI__Expert 4680 points

    Hi Steven,

    Thanks for the update.

    We are not interested in adjusting the O/P current based on PWM ..we are interested in turning on off the LED’s (strip of 12 LED  in series 5A current through the strip turned on for 100 us with the current limited to 5A and off for 900us for 40 pulses at 1ms period or 1000 FPS  after  every 1S of idle time  this 40 pulse train will repeat . The forward voltage of individual LED is 3.9 V at 5A so the o/p voltage is 46.8 V i/p voltage will be 5 -55 V

  • 0 in reply to Ernest Yong
    TI__Mastermind 23245 points

    Hi Ernest,

    If the input voltage is 5 - 55V, and the LED voltage is 46.8V, then TPS923655 cannot do this even if you configure if in the buck-boost connection.

    The output voltage should be no more than 63V. (Please refer to Section 7.3 Recommended Operating Conditions from the datasheet.) The switching FET cycle-by-cycle current limit also cannot support 5A output in such a condition. (Please refer to Section 7.5 Electrical Characteristics from the datasheet.)

    May I understand why the input voltage varies in such a large range? If the input voltage can be fixed to be larger than LED voltage plus some margin, like 55V, then it is possible for TPS922055 to achieve such kind of output requirement. We can talk through e-mail if needed.

    Best Regards,

    Steven