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LSF010XEVM-001 doesn't work, why?

Other Parts Discussed in Thread: LSF0101

Hi,

     I am using the LSF010XEVM-001 to do a digital signal level translation from 3.3V to 1.2V.  We do it exactly asthe data sheet.

    For example, for LSF0101,  the P1.1 is connected to 3.3V, P1.2 (VrefA) is connect to 1.2V, P1.3(VAPU) is connected to 1.2V, P2.1 is connected to GND, P2.2(VrefB) is connected to 3.3V, P2.3 (VBPU) is connected to 3.3 V.  

   However, in this configuration, we notice the VrefA will be driven to 1.7V and there are large current (40mA) in VrefA and VrefB.

   The A1 signal is also not correct (about 2V when B1 is 3.3V).

   All the input signals are generated by signal generator (HP-E3631A).

  I don't know why it doesn't work and can anybody help me to fix it?

  Thanks  a lot!

  

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  • Hi You Li ,
    With B1 signal being driven by signal generator which is a push pull , there is no requirement for VBPU of 3.3V . You can directly connect B1 signal into P1.4 and observe output on A side .
    You may also get away with VAPU since you are pulling up same voltage upto VrefA and have current sink at the output too .
  • Hi Shreyas

         Thanks for your reply!

         However, it doesn't work even if I remove the input of VBPU or VAPU or both of them, (Let the them floating). The output in A side is not in the 1.2V level as expected and it goes to about 1.6-1.7V.   Moreover,  if I use signal generator to generate the VrefA =1.2 and VrefB=3.3  and give them to the P1.2 and P2.2, the VrefA will be pulled about 1.6 V and there are large current (~40mA) in VrefA and VrefB. It looks like the VrefA and VrefB are shorted by some path in the circuit.

         I don't know why and could you please help me to fix it ?

         Thank you very much!

          You (Leo) Li 

  • Hi You Li,
    Alright , the LSF is a simple nmos passive switch which doesn't have its output drive . Can you connect signal from the signal generator at 3.3V into A1 pin and have VBPU to 1.2V and see the response ? As the inputs rises above the Vref-0.5V(1.2-0.5=0.7V ) , the switch starts turning off and the B side pull up resistor should pull output to 1.2V .No VAPU connection since the signal generator can output 0-3.3V .

    You can also send in your connection schematics if available .