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LSF0108: LSF0108 unused pin and PCB layout

Andrew Du
Intellectual 1840 points
Part Number: LSF0108

HI, Gentlemen:

My customer use LSF0108 and have two questions:

1. to the unused input/output pin, if they can leave it float or must connect to the GND?

2. In the PCB layout guide, suggest put the LSF0108 devcie close to the hige voltage side, why? In current design, The distance between LSF to high voltage side is 4200mil and the data rate is 10MHz, is it ok or not?

Thanks! 

  • 0
    TI__Mastermind 24975 points
    Hello Andrew,

    1. It is recommended to tie at least one port on each unused channel to ground to avoid leaving a pin floating (either the A or B side is fine). The reason for this is to avoid having a pin on the device with an unknown voltage level. Only one side of the unused channel needs to be tied to ground, but both can be because the LSF does not produce current.
    If you are not using the channel at all, you may GND both sides of the device for that channel.

    2. It says to place closer to the high voltage side because additional drive is required to get the output high voltage, so a cleaner signal will result on the high voltage side.
    If you have a 4200 mil trace and 10MHz, the device should be able to drive this. As long as the trace capacitance is the only capacitance and there is no external capacitor, there should be no issues.

    Best,
    Michael