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LSF0108 200k resistor to VEREFB-EN

Christos Karatzoglou
Intellectual 405 points
Other Parts Discussed in Thread: LSF0108

Hallo,

I have described my configuration to a previous post e2e.ti.com/.../547629.

Basically I want to implement a voltage transltor form 3.3 V (Push-pull) to 5 V (opendrain 1.6k).Up to now the desgin is working pretty good and stable using LSF0108. In total I am using 6 lines with relatively long cables (up to 2m) but my signal frequency is relatively small (150 KHz). Today Iam starting to have some problems with some of the lines and I suspect that the duration of the pulses is not translated correctly. I just also realize that I have forgotten to put a 200k resistor between 5 V and VERFB-EN they both connected directly to 5 V, can it be the cause of the problem?

What is wired is that only some lines have problems and the rest of them are working fine. I have already performed a lot of tests for more than twenty days and I had never seen a problem.

Any ideas?

  • 0
    TI__Guru 62160 points
    Hi Christos ,

    Without a 200k resistor between power supply and VrefB pin, you would basically be connecting a 5V supply to the 3.3V supply and the internal FET will be heavily biased with higher than normal current consumption.
    The gate of the channels will be biased to 5V and not the desired voltage with respect to VrefA . would suggest to have the 200K to bias the FET right for proper operation.