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Original question:

TPS92512HV: Why is the output capacitor not connected to GND?

TPS92512HV: What does it mean if COMP pin measures 1V?

Brian Josel
Intellectual 320 points
Part Number: TPS92512HV

I have Rt = 162k, and I measure my switching frequency to be approx 714kHz, so I am in the neighborhood.  My PDIM function is performing nominally, 1200us ON every 120Hz.  Rsense set to 150mOhms to get LED current = 2A.  

Why does my COMP pin measure 1V?  The datasheet says it should read 0.7V, but that is not the case.  What does it mean if the COMP pin measures 1V?

  • 0
    Intellectual 320 points
    Ccomp = 0.1uF in my design
  • 0 in reply to Brian Josel
    TI__Mastermind 28655 points
    Hello Brian,

    Are you referring to the start-up. 0.7 volts is when the comp allows the IC to become active and switch. Comp will move depending on what is needed to regulate your output current. Once it hits 0.7 it tries to start and the voltage increases on Comp until regulation is met. Start-up is in 8.4.1 of the datasheet. 1V in your design must be where it needs to be to regulate. If you change operating conditions the Comp voltage may change if it needs to.

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Intellectual 320 points

    Is there any way to determine what Vcomp should measure based on my operating conditions?

  • 0 in reply to Brian Josel
    TI__Mastermind 28655 points
    Hello Brian,

    If it is regulating current the compensation voltage is where is should be. It will vary depending on operating conditions. This is similar to an integrating op-amp circuit. It will stabilize when the circuit reaches equilibrium. Some times this is dynamic, such as when you are PWMing the IC, changing Viadj, the input changes or the output changes, then the error amplifier has to adjust, on input to this is Comp. Is there a reason to know what the voltage is? If it is regulating current correct it's working correct.

    Best Regards,