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TPS92691: Load current start-up behavior with TPS92691

Feng bin Su
Expert 8690 points
Part Number: TPS92691

Hi team,

My customer is using our LED driver TPS92691 to do a load current startup measurement and the waveform is as below figure.

CH1:Vout, CH2:GATE(pin15), CH4: Iout

When the Gate is turned on in the initial stage (about 13us) How can we control it and how to shorten the time?

Or it is reasonable behavior for you?

  • 0
    TI__Mastermind 18890 points

    Hello,

    Is the waveform above happening when PWM is first driven high or what is the condition?

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    TI__Expert 8690 points

    Hi Tuan,

    It is first heavy load transient condition and Vout has sustain at 50v for a while. Thanks.

    Ben,

  • 0 in reply to Feng bin Su
    TI__Mastermind 18890 points

    Hello Feng,

    I believe your answer is that PWM is going High during this time.  This is a normal operation of the TPS92691.  When PWM is forced to a logic low state, the TPS92691 will turns off the switching and tri-state the COMP pin to maintain the voltage on the compensation network and disable the PWM Dimming FET.  Then on the next rising edge of the PWM input, the gate and DDRV outputs are enable to ramp the inductor current to the previous steady state value.  During this ramping time the gate to the switching FET is turned on until VIS reaches the previous COMP voltage.  Please see section 7.3.8 of the specification.  From your scope capture this is the 13uS time. 

    We do this as a way to reach the previous inductor current faster so LED current can be ramp to command current faster.

    Thanks Tuan