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TPS92512: About Start up

Koji Hayashi92
Mastermind 7030 points
Part Number: TPS92512
Other Parts Discussed in Thread: LM3409, TPS92515,

Hi All

After turning on the power, I am in trouble that the time(Tdelay） for PDIM to switch from L to H to regulation mode is long.

Is it okay to make Ccomp smaller ? Is there any other way to shorten the time ?

Fig.14 of DataSheet is not the first waveform after startup but is the waveform at stabilization ?

COMP is 0 V after turning on the power supply, but it is controlled by SWITCH during stabilization.

I understand from the Functional Block Diagram of DataSheet that the voltage does not decrease.

Best Regards,

Koji Hayashi

  • 0
    TI__Mastermind 28655 points
    Hello Koji,

    You can make Ccomp smaller as long as it is stable over your operating conditions and design. You could also look at a type two compensation. Another option is to precharge comp when first powered on to 0.6V or so. If you are PWM dimming during power up you can delay the PWM and leave high until comp charges partially. You can also look at the TPS92515 or LM3409 which are hysteretic controllers and will power up quicker.

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Mastermind 7030 points
    Hi Irwin-san

    Thank you for quick response.
    Please tell me the link of the type2 document file.
    Also, please tell me the circuit configuration for precharge.
    First, I will examine the above two patterns.
    In case it is difficult, I propose TPS92515 and LM3409 to my customer.

    Best Regards,
    Koji Hayashi
  • 0 in reply to Koji Hayashi92
    TI__Mastermind 28655 points

    Hello Koji,

    8.3.6 shows the equation for BW.  It also state you may be able to use a value of Ccomp down to 0.01 uF.


    Here is a link to type 2 and type 3 compensators: www.ti.com/.../getliterature.tsp A loop analyzer is probably the easiest to implement this.

    If they want to pre-charge the compensation capacitor a current mirror (two transistors and some resistors) and a fixed voltage such as five volts will work though it adds quite a few components. The idea is to set the current mirror up to allow the compensation side to provide current up to about 0.6V then allow the TPS92512 to take over reverse biasing the transistor, this will take a little design work.

    Are they trying to power up while PWMing?

    They can also try lowering the capacitance value and making sure the TPS92512 is still stable over their operating range.

    A hysteretic part is a much easier way of implementing this.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Mastermind 7030 points

    HI Irwin-san

    Thank you for respopnse.

    I saw SLVA662.

    For Type II, I think R2 and C1 are necessary for calculation.

    Do you know the values of R2 and C1 ?
    Best Regards,
    Koji Hayashi
  • 0 in reply to Koji Hayashi92
    TI__Mastermind 28655 points
    Hello Koji,

    Those values are part of the loop compensation. This depends on their application. It would be best to use a loop analyzer and run the driver at all corner conditions to make sure the loop is stable over their entire operating range. This can be done to a lesser extent by looking at transient response at all operating conditions as well. When I do it this way I increase the bandwidth until is becomes somewhat unstable then back off an appropriate amount to ensure some margin.

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Mastermind 7030 points

    Hi Irwin-san

    Thank you for quick response.

    I understand.

    I will tell customers that it is necessary to confirm stability with actual measurement.

    Best Regards,

    Koji Hayashi