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TPS92612-Q1: TPS92612 Running at Higher Frequencies

Damian Aceves-Franco
Prodigy 10 points
Part Number: TPS92612-Q1
Other Parts Discussed in Thread: TPS92612

Hello TI Support,

I want to use the TPS92612 in a design. I would like to run it above 20Khz but lower than 100KHz. Would this be possible to do with the TPS92612. 

What are the limitation when you run it at these frequencies. Below is the my current configuration.  R(sns) is 1ohm,  R(p) is 75ohm and the NPN is a simple 2222 transistor with a 4.6K base resistor. 

By desired current is 100mA. If the higher frequencies are an issue, Why are they?

  • +1
    TI__Expert 4970 points

    Hello,

    Why are you proposing tie the PWM input into a transistor at the bottom of the string as well as the PWM input pin? 

    Best, 

    Pedro Arango Ramirez.

  • 0 in reply to Pedro Arango Ramirez
    Prodigy 10 points

    Hello Pedro,

    This diagram in is the datasheet. I suppose the purpose is to make sure the LEDs are off or on when when the PWM is low or high. 

    I'm not sure why TI did it this way but it works. 

    Back to my question I'm having trouble running the TPS92612 at higher frequencies. 

    Thanks,

    -Damian

  • 0 in reply to Damian Aceves-Franco
    TI__Expert 4970 points

    Hello Damian, I see. That is quite different from how the EVM is implemented but I digress. Your frequency is going to mostly be limited by the rise and fall times of the PWM voltage rising edge. If the frequency is faster than the PWM voltage rising time then it is possible that the current in the LED will be affected by the slew rate of the voltage, meaning that the total current will not simply be a function of averaged duty cycle but also average duty cycle plus slew rate. I would recommend staying in a frequency that makes the rising times of PWM (as well as diagnostics) negligible to that of the PWM input frequency

    At 20Khz the period will be 50uS which is considerably close to the rise and fall time of the PWM delay. Without considering the turn on and off times of the FET this is already quite higher than what the device can handle. This is why in section 7.3.3 of the datasheet TI recommends keeping the PWM control between 200Hz and 2kHz. I do not believe that this high frequency application can be implemented.

    Best,

    Pedro Arango Ramirez.