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LSF0108: Application for LPC signal

Shu-Cheng LIN
Guru 11785 points
Part Number: LSF0108

Hi Sirs,

Sorry to bother you.

We have use LSF0108 on LPC signal.

Schematic:

There had 330 ohm pull resister on both side.

We saw  LPCCLK and LPCCLK1 on 1.8V to 3.3V has been from the square wave to triangular wave (Figure 2), and from the DATA SHEET inside the Waveform can also see this phenomenon (Figure 3)
Would you like to have a way to improve?

Fig 2

Fig 3

The second question, how do design if our output not only connect one device?

  • 0
    Guru 317370 points
    LSF devices are passive switches, so the shape of the rising edge is determined by the RC filter created by the pull-up resistor and the parasitic capacitances.

    To get faster edges, use a smaller pull-up resistor (if your devices have enough drive strength), or change the circuit layout to reduce the parasitic capacitances.
  • 0 in reply to Clemens Ladisch
    TI__Mastermind 24985 points

    As Clemens mentioned, the output rise time is depending on the RC on the output. If you want faster edge rates on step-up translation, then you should decrease the size of your pullup resistor. 

    Additionally, if you want to drive multiple devices, then this will simply contribute to the parasitic capacitances that are on the line. To drive more devices, a lower pullup resistor is needed.

    Best,
    Michael